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7-1-1. National Weather Service Aviation
Products
a. Weather service to aviation is a joint effort of the
National Weather Service (NWS), the Federal
Aviation Administration (FAA), the military weather
services, and other aviation oriented groups and
individuals. The NWS maintains an extensive
surface, upper air, and radar weather observing
program; a nationwide aviation weather forecasting
service; and provides limited pilot briefing service
(interpretational). The majority of pilot weather
briefings are provided by FAA personnel at Flight
Service Stations (AFSSs/FSSs). Aviation routine
weather reports (METAR) are taken manually by
NWS, FAA, contractors, or supplemental observers.
METAR reports are also provided by Automated
Weather Observing System (AWOS) and Automated
Surface Observing System (ASOS).
REFERENCE-
AIM, Para
7-1-12, Weather Observing Programs.
b. Aerodrome forecasts are prepared by approximately 100 Weather Forecast Offices (WFOs). These
offices prepare and distribute approximately
525 aerodrome forecasts 4 times daily for specific
airports in the 50 States, Puerto Rico, the Caribbean
and Pacific Islands. These forecasts are valid for
24 hours and amended as required. WFOs prepare
over 300 route forecasts and 39 synopses for
Transcribed Weather Broadcasts (TWEB), and
briefing purposes. The route forecasts are issued
4 times daily, each forecast is valid for 12 hours. A
centralized aviation forecast program originating
from the Aviation Weather Center (AWC) in Kansas
City was implemented in October 1995. In the
conterminous U.S., all Inflight Advisories Significant Meteorological Information (SIGMETs),
Convective SIGMETs, and Airmen's Meteorological
Information (AIRMETs) and all Area Forecasts
(FAs) (6 areas) are now issued by AWC. FAs are
prepared 3 times a day in the conterminous U.S. and
Alaska (4 times in Hawaii), and amended as required.
Inflight Advisories are issued only when conditions
warrant. Winds aloft forecasts are provided for
176 locations in the 48 contiguous States and
21 locations in Alaska for flight planning purposes.
(Winds aloft forecasts for Hawaii are prepared
locally.) All the aviation weather forecasts are given
wide distribution through the Weather Message
Switching Center Replacement (WMSCR) in
Atlanta, Georgia, and Salt Lake City, Utah.
REFERENCE-
AIM, Para
7-1-6, Inflight Aviation Weather Advisories.
c. Weather element values may be expressed by
using different measurement systems depending on
several factors, such as whether the weather products
will be used by the general public, aviation interests,
international services, or a combination of these
users.
FIG 7-1-1 provides conversion tables for the
most used weather elements that will be encountered
by pilots.
7-1-2. FAA Weather Services
a. The FAA maintains a nationwide network of
Automated Flight Service Stations (AFSSs/FSSs) to
serve the weather needs of pilots. In addition, NWS
meteorologists are assigned to most ARTCCs as part
of the Center Weather Service Unit (CWSU). They
provide Center Weather Advisories (CWAs) and
gather weather information to support the needs of
the FAA and other users of the system.
b. The primary source of preflight weather
briefings is an individual briefing obtained from a
briefer at the AFSS/FSS. These briefings, which are
tailored to your specific flight, are available 24 hours
a day through the use of the toll free number
(1-800-WX BRIEF). Numbers for these services can
be found in the Airport/Facility Directory (A/FD)
under "FAA and NWS Telephone Numbers" section.
They may also be listed in the U.S. Government
section of your local telephone directory under
Department of Transportation, Federal Aviation
Administration, or Department of Commerce,
National Weather Service. NWS pilot weather
briefers do not provide aeronautical information
(NOTAMs, flow control advisories, etc.) nor do they
accept flight plans.
REFERENCE-
AIM, Para
7-1-4, Preflight Briefing, explains the types of preflight
briefings available and the information contained in each.
FIG 7-1-1
Weather Elements Conversion Tables
c. Other Sources of Weather Information
1. Telephone Information Briefing Service
(TIBS) (AFSS); and in Alaska, Transcribed Weather
Broadcast (TWEB) locations, and telephone access
to the TWEB (TEL-TWEB) provide continuously
updated recorded weather information for short or
local flights. Separate paragraphs in this section give
additional information regarding these services.
REFERENCE-
AIM, Telephone Information Briefing Service (TIBS), Paragraph
7-1-8.
AIM, Transcribed Weather Broadcast (TWEB) (Alaska Only),
Paragraph 7-1-9.
2. Weather and aeronautical information are
also available from numerous private industry
sources on an individual or contract pay basis.
Information on how to obtain this service should be
available from local pilot organizations.
3. The Direct User Access Terminal System (DUATS) can be accessed by pilots with a
current medical certificate toll-free in the 48 contiguous States via personal computer. Pilots can receive
alpha-numeric preflight weather data and file
domestic VFR and IFR flight plans. The following
are the contract DUATS vendors:
GTE Federal Systems
15000 Conference Center Drive
Chantilly, VA 22021-3808
Computer Modem Access Number: For filing flight
plans and obtaining weather briefings:
(800) 767-9989
For customer service: (800) 345-3828
Data Transformation Corporation
108-D Greentree Road
Turnersville, NJ 08012
Computer Modem Access Number: For filing flight
plans and obtaining weather briefings:
(800) 245-3828
For customer service: (800) 243-3828
d. Inflight weather information is available from
any FSS within radio range. The common frequency
for all AFSSs is 122.2. Discrete frequencies for
individual stations are listed in the A/FD.
1. Information on In-Flight Weather broadcasts.
REFERENCE-
AIM, Inflight Weather Broadcasts, Paragraph
7-1-10.
2. En Route Flight Advisory Service (EFAS) is
provided to serve the nonroutine weather needs of
pilots in flight.
REFERENCE-
AIM, En Route Flight Advisory Service (EFAS), Paragraph
7-1-5, gives
details on this service.
7-1-3. Use of Aviation Weather Products
a. Air carriers and operators certificated under the
provisions of 14 CFR Part 119 are required to use the
aeronautical weather information systems defined in
the Operations Specifications issued to that certificate holder by the FAA. These systems may utilize
basic FAA/National Weather Service (NWS) weather
services, contractor- or operator-proprietary weather services and/or Enhanced Weather Information
System (EWINS) when approved in the Operations
Specifications. As an integral part of this system
approval, the procedures for collecting, producing
and disseminating aeronautical weather information,
as well as the crew member and dispatcher training to
support the use of system weather products, must be
accepted or approved.
b. Operators not certificated under the provisions
of 14 CFR Part 119 are encouraged to use FAA/NWS
products through Flight Service Stations, Direct User
Access Terminal System (DUATS), and/or Flight
Information Services Data Link (FISDL).
c. The suite of available aviation weather product
types is expanding, with the development of new
sensor systems, algorithms and forecast models. The
FAA and NWS, supported by the National Center for
Atmospheric Research and the Forecast Systems
Laboratory, develop and implement new aviation
weather product types through a comprehensive
process known as the Aviation Weather Technology
Transfer process. This process ensures that user needs
and technical readiness requirements are met before
experimental products mature to operational
application.
d. The FAA, in conjunction with the NWS,
established the Aviation Weather Technology
Transfer (AWTT) Board so that newly developed
aviation weather products meet regulatory
requirements and enhance safety. The AWTT is
charged with managing and accelerating the transfer
of these products into operational use. Members of
the AWTT Board include mid-level managers from
the FAA and NWS who are responsible for various
aspects of the development and use of aviation
weather products (e.g., aviation weather R & D,
transition of weather products from R & D to
operational use, etc.).
e. The AWTT is a management-review and
decision-making process that applies criteria to
weather products at various development stages
(decision stages, i.e., "D-stages"). The D-stages are
composed of the following:
1. (D1) Sponsorship of user needs.
2. (D2) R & D and controlled testing.
3. (D3) Experimental application.
4. (D4) Operational application.
f. Weather products maturing into the D3
experimental stage of the AWTT process are often
made available to the public on the Aviation Weather
Center's Experimental Aviation Digital Data Service
(ADDS) website at: http://weather.aero/. The intent
is to allow public access to this information in order
to obtain feedback for product development and
improvement. However, it is important to note that
weather products displayed on this site are
experimental, and although they may appear to be
fully operational products, they are subject to change
without notification and may not be used for any
flight related decisions. At the D4 stage, the FAA
approves a weather product for operational use by
end users (with restrictions, if necessary), and the
product is made available to the public via long-line
circuit, satellite, and/or other means of
communication.
g. Pilots and operators should be aware that
weather services provided by entities other than FAA,
NWS or their contractors (such as the DUATS and
FISDL providers) may not meet FAA/NWS quality
control standards. Hence, operators and pilots
contemplating using such services should request
and/or review an appropriate description of services
and provider disclosure. This should include, but is
not limited to, the type of weather product (e.g.,
current weather or forecast weather), the currency of
the product (i.e., product issue and valid times), and
the relevance of the product. Pilots and operators
should be cautious when using unfamiliar products,
or products not supported by FAA/NWS technical
specifications.
NOTE-
When in doubt, consult with a FAA Flight Service Station
Specialist.
h. In addition, pilots and operators should be
aware there are weather services and products
available from government organizations beyond the
scope of the AWTT process mentioned earlier in this
section. For example, governmental agencies such as
the NWS, the Aviation Weather Center (AWC), and
the National Center for Atmospheric Research
(NCAR) display weather "model data" and
"experimental" products which require training
and/or expertise to properly interpret and use. These
products are developmental prototypes that are
subject to ongoing research and can change without
notice. Therefore, some data on display by
government organizations, or government data on
display by independent organizations may be
unsuitable for flight planning purposes. Operators
and pilots contemplating using such services should
request and/or review an appropriate description of
services and provider disclosure. This should include,
but is not limited to, the type of weather product (e.g.,
current weather or forecast weather), the currency of
the product (i.e., product issue and valid times), and
the relevance of the product. Pilots and operators
should be cautious when using unfamiliar weather
products.
NOTE-
When in doubt, consult with a FAA Flight Service Station
Specialist.
i. The development of new weather products
coupled with increased access to these products via
the public Internet, created confusion within the
aviation community regarding the relationship
between regulatory requirements and new weather
products. Consequently, FAA differentiates between
those weather products that may be utilized to comply
with regulatory requirements and those that may only
be used to improve situational awareness. To clarify
the proper use of aviation weather products to meet
the requirements of 14 CFR, FAA defines weather
products as follows:
1. Primary Weather Product. An aviation
weather product that meets all the regulatory
requirements and safety needs for use in making
flight related, aviation weather decisions.
2. Supplementary Weather Product. An
aviation weather product that may be used for
enhanced situational awareness. If utilized, a
supplementary weather product must only be used in
conjunction with one or more primary weather
product. In addition, the FAA may further restrict the
use of supplementary aviation weather products
through limitations described in the product label.
NOTE-
An aviation weather product produced by the Federal
Government and managed by the AWTT is classified a
primary weather product unless designated a
supplementary weather product by the FAA.
j. In developing the definitions of primary and
supplementary weather products, it is not the intent of
FAA to change or increase the regulatory burden on
the user. Rather, the definitions are meant to eliminate
confusion by differentiating between weather
products that may be utilized to meet regulatory
requirements and other weather products that may
only be used to improve situational awareness.
k. All flight-related, aviation weather decisions
must be based on primary weather products.
Supplementary weather products augment the
primary products by providing additional weather
information but may not be used as stand-alone
weather products to meet aviation weather regulatory
requirements or without the relevant primary
products. When discrepancies exist between primary
and supplementary weather products describing the
same weather phenomena, users must base flight-related decisions on the primary weather product.
Furthermore, multiple primary products may be
necessary to meet all aviation weather regulatory
requirements.
l. The development of enhanced communications
capabilities, most notably the Internet, has allowed
pilots access to an ever-increasing range of weather
service providers and proprietary products. The FAA
has identified three distinct types of weather
information available to pilots and operators.
1. Observations. Raw weather data collected
by some type of sensor suite including surface and
airborne observations, radar, lightning, satellite
imagery, and profilers.
2. Analysis. Enhanced depiction and/or
interpretation of observed weather data.
3. Forecasts. Predictions of the development
and/or movement of weather phenomena based on
meteorological observations and various
mathematical models.
m. Not all sources of aviation weather information
are able to provide all three types of weather
information. The FAA has determined that operators
and pilots may utilize the following approved sources
of aviation weather information:
1. Federal Government. The FAA and NWS
collect raw weather data, analyze the observations,
and produce forecasts. The FAA and NWS
disseminate meteorological observations, analyses,
and forecasts through a variety of systems. In
addition, the Federal Government is the only
approval authority for sources of weather
observations; for example, contract towers and
airport operators may be approved by the Federal
Government to provide weather observations.
2. Enhanced Weather Information System
(EWINS). An EWINS is an FAA approved,
proprietary system for tracking, evaluating,
reporting, and forecasting the presence or lack of
adverse weather phenomena. An EWINS is
authorized to produce flight movement forecasts,
adverse weather phenomena forecasts, and other
meteorological advisories. For more detailed
information regarding EWINS, see the Aviation
Weather Services Advisory Circular 00-45 and the
Air Transportation Operations Inspector's
Handbook 8400.10.
3. Commercial Weather Information
Providers. In general, commercial providers
produce proprietary weather products based on
NWS/FAA products with formatting and layout
modifications but no material changes to the weather
information itself. This is also referred to as
"repackaging." In addition, commercial providers
may produce analyses, forecasts, and other
proprietary weather products that substantially alter
the information contained in government-produced
products. However, those proprietary weather
products that substantially alter government-produced weather products or information, may only
be approved for use by 14 CFR Part 121 and Part 135
certificate holders if the commercial provider is
EWINS qualified.
NOTE-
Commercial weather information providers contracted by
FAA to provide weather observations, analyses, and
forecasts (e.g., contract towers) are included in the Federal
Government category of approved sources by virtue of
maintaining required technical and quality assurance
standards under Federal Government oversight.
n. As a point of clarification, Advisory
Circular 00-62, Internet Communications of
Aviation Weather and NOTAMS, describes the
process for a weather information provider to become
a Qualified Internet Communications Provider
(QICP) and only applies to 14 CFR Part 121 and
Part 135 certificate holders. Therefore, pilots
conducting operations under 14 CFR Part 91 may
access weather products via the public Internet.
7-1-4. Preflight Briefing
a. Flight Service Stations (AFSSs/FSSs) are the
primary source for obtaining preflight briefings and
inflight weather information. Flight Service Specialists are qualified and certificated by the NWS as Pilot
Weather Briefers. They are not authorized to make
original forecasts, but are authorized to translate and
interpret available forecasts and reports directly into
terms describing the weather conditions which you
can expect along your flight route and at your
destination. Available aviation weather reports,
forecasts and aviation weather charts are displayed at
each AFSS/FSS, for pilot use. Pilots should feel free
to use these self briefing displays where available, or
to ask for a briefing or assistance from the specialist
on duty. Three basic types of preflight briefings are
available to serve your specific needs. These are:
Standard Briefing, Abbreviated Briefing, and
Outlook Briefing. You should specify to the briefer
the type of briefing you want, along with your
appropriate background information. This will
enable the briefer to tailor the information to your
intended flight. The following paragraphs describe
the types of briefings available and the information
provided in each briefing.
REFERENCE-
AIM, Preflight Preparation, Paragraph
5-1-1, for items that are
required.
b. Standard Briefing. You should request a
Standard Briefing any time you are planning a flight
and you have not received a previous briefing or have
not received preliminary information through mass
dissemination media; e.g., TIBS, TWEB (Alaska
only), etc. International data may be inaccurate or
incomplete. If you are planning a flight outside of
U.S. controlled airspace, the briefer will advise you
to check data as soon as practical after entering
foreign airspace, unless you advise that you have the
international cautionary advisory. The briefer will
automatically provide the following information in
the sequence listed, except as noted, when it is
applicable to your proposed flight.
1. Adverse Conditions. Significant meteorological and aeronautical information that might
influence the pilot to alter the proposed flight;
e.g., hazardous weather conditions, airport closures,
air traffic delays, etc.
2. VFR Flight Not Recommended. When
VFR flight is proposed and sky conditions or
visibilities are present or forecast, surface or aloft,
that in the briefer's judgment would make flight
under visual flight rules doubtful, the briefer will
describe the conditions, affected locations, and use
the phrase "VFR flight not recommended." This
recommendation is advisory in nature. The final
decision as to whether the flight can be conducted
safely rests solely with the pilot.
3. Synopsis. A brief statement describing the
type, location and movement of weather systems
and/or air masses which might affect the proposed
flight.
NOTE-
These first 3 elements of a briefing may be combined in any
order when the briefer believes it will help to more clearly
describe conditions.
4. Current Conditions. Reported weather
conditions applicable to the flight will be summarized
from all available sources; e.g., METARs/ SPECIs,
PIREPs, RAREPs. This element will be omitted if the
proposed time of departure is beyond 2 hours, unless
the information is specifically requested by the pilot.
5. En Route Forecast. Forecast en route
conditions for the proposed route are summarized in
logical order; i.e., departure/climbout, en route, and
descent. (Heights are MSL, unless the contractions
"AGL" or "CIG" are denoted indicating that heights
are above ground.)
6. Destination Forecast. The destination forecast for the planned ETA. Any significant changes
within 1 hour before and after the planned arrival are
included.
7. Winds Aloft. Forecast winds aloft will be
provided using degrees of the compass. The briefer
will interpolate wind directions and speeds between
levels and stations as necessary to provide expected
conditions at planned altitudes. (Heights are MSL.)
Temperature information will be provided on request.
8. Notices to Airmen (NOTAMs).
(a) Available NOTAM (D) information pertinent to the proposed flight.
(b) NOTAM (L) information pertinent to the
departure and/or local area, if available, and pertinent
FDC NOTAMs within approximately 400 miles of
the FSS providing the briefing. AFSS facilities will
provide FDC NOTAMs for the entire route of flight.
(c) FSS briefers do not provide FDC NOTAM
information for special instrument approach procedures unless specifically asked. Pilots authorized by
the FAA to use special instrument approach
procedures must specifically request FDC NOTAM
information for these procedures.
NOTE-
NOTAM information may be combined with current
conditions when the briefer believes it is logical to do so.
NOTE-
NOTAM (D) information and FDC NOTAMs which have
been published in the Notices to Airmen Publication are
not included in pilot briefings unless a review of this
publication is specifically requested by the pilot. For
complete flight information you are urged to review the
printed NOTAMs in the Notices to Airmen Publication and
the A/FD in addition to obtaining a briefing.
9. ATC Delays. Any known ATC delays and
flow control advisories which might affect the
proposed flight.
10. Pilots may obtain the following from
AFSS/FSS briefers upon request:
(a) Information on Special Use Airspace
(SUA), SUA related airspace and Military Training
Routes (MTRs) activity within the flight plan area
and a 100 NM extension around the flight plan area.
NOTE-
1. SUA and related airspace includes the following types
of airspace: Alert Area, Military Operations Area (MOA),
Prohibited Area, Restricted Area, Refueling Anchor,
Warning Area and Air Traffic Control Assigned Airspace
(ATCAA). MTR data includes the following types of
airspace: IFR Military Training Route (IR), VFR Military
Training Route (VR), Slow Training Route (SR) and Aerial
Refueling Track (AR).
2. Pilots are encouraged to request updated information
from ATC facilities while in flight.
(b) A review of the Notices to Airmen
Publication for pertinent NOTAMs and Special
Notices.
(c) Approximate density altitude data.
(d) Information regarding such items as air
traffic services and rules, customs/immigration
procedures, ADIZ rules, search and rescue, etc.
(e) LORAN-C NOTAMs, available military
NOTAMs, and runway friction measurement value
NOTAMs.
(f) GPS RAIM availability for 1 hour before
to 1 hour after ETA or a time specified by the pilot.
(g) Other assistance as required.
c. Abbreviated Briefing. Request an Abbreviated Briefing when you need information to
supplement mass disseminated data, update a
previous briefing, or when you need only one or two
specific items. Provide the briefer with appropriate
background information, the time you received the
previous information, and/or the specific items
needed. You should indicate the source of the
information already received so that the briefer can
limit the briefing to the information that you have not
received, and/or appreciable changes in meteorological/aeronautical conditions since your previous
briefing. To the extent possible, the briefer will
provide the information in the sequence shown for a
Standard Briefing. If you request only one or two
specific items, the briefer will advise you if adverse
conditions are present or forecast. (Adverse conditions contain both meteorological and/or aeronautical
information.) Details on these conditions will be
provided at your request. International data may be
inaccurate or incomplete. If you are planning a flight
outside of U.S. controlled airspace, the briefer will
advise you to check data as soon as practical after
entering foreign airspace, unless you advise that you
have the international cautionary advisory.
d. Outlook Briefing. You should request an
Outlook Briefing whenever your proposed time of
departure is six or more hours from the time of the
briefing. The briefer will provide available forecast
data applicable to the proposed flight. This type of
briefing is provided for planning purposes only. You
should obtain a Standard or Abbreviated Briefing
prior to departure in order to obtain such items as
adverse conditions, current conditions, updated
forecasts, winds aloft and NOTAMs, etc.
e. When filing a flight plan only, you will be asked
if you require the latest information on adverse
conditions pertinent to the route of flight.
f. Inflight Briefing. You are encouraged to
obtain your preflight briefing by telephone or in
person before departure. In those cases where you
need to obtain a preflight briefing or an update to a
previous briefing by radio, you should contact the
nearest AFSS/FSS to obtain this information. After
communications have been established, advise the
specialist of the type briefing you require and provide
appropriate background information. You will be
provided information as specified in the above
paragraphs, depending on the type briefing requested. In addition, the specialist will recommend
shifting to the Flight Watch frequency when
conditions along the intended route indicate that it
would be advantageous to do so.
g. Following any briefing, feel free to ask for any
information that you or the briefer may have missed
or are not understood. This way, the briefer is able to
present the information in a logical sequence, and
lessens the chance of important items being
overlooked.
7-1-5. En Route Flight Advisory Service
(EFAS)
a. EFAS is a service specifically designed to
provide en route aircraft with timely and meaningful
weather advisories pertinent to the type of flight
intended, route of flight, and altitude. In conjunction
with this service, EFAS is also a central collection and
distribution point for pilot reported weather information. EFAS is provided by specially trained specialists
in selected AFSSs controlling multiple Remote
Communications Outlets covering a large geographical area and is normally available throughout the
conterminous U.S. and Puerto Rico from 6 a.m. to
10 p.m. EFAS provides communications capabilities
for aircraft flying at 5,000 feet above ground level to
17,500 feet MSL on a common frequency of
122.0 MHz. Discrete EFAS frequencies have been
established to ensure communications coverage from
18,000 through 45,000 MSL serving in each specific
ARTCC area. These discrete frequencies may be used
below 18,000 feet when coverage permits reliable
communication.
NOTE-
When an EFAS outlet is located in a time zone different from
the zone in which the flight watch control station is located,
the availability of service may be plus or minus one hour
from the normal operating hours.
b. In some regions of the contiguous U.S.,
especially those that are mountainous, it is necessary
to be above 5000 feet AGL in order to be at an altitude
where the EFAS frequency, 122.0 MHz, is available.
Pilots should take this into account when flight
planning. Other AFSS communication frequencies
may be available at lower altitudes. See
FIG 7-1-2.
c. Contact flight watch by using the name of the
ARTCC facility identification serving the area of
your location, followed by your aircraft identification, and the name of the nearest VOR to your
position. The specialist needs to know this
approximate location to select the most appropriate
transmitter/receiver outlet for communications
coverage.
EXAMPLE-
Cleveland Flight Watch, Cessna One Two Three Four Kilo,
Mansfield V-O-R, over.
d. Charts depicting the location of the flight watch
control stations (parent facility) and the outlets they
use are contained in the A/FD. If you do not know in
which flight watch area you are flying, initiate contact
by using the words "Flight Watch," your aircraft
identification, and the name of the nearest VOR. The
facility will respond using the name of the flight
watch facility.
EXAMPLE-
Flight Watch, Cessna One Two Three Four Kilo,
Mansfield V-O-R, over.
e. AFSSs that provide En Route Flight Advisory
Service are listed regionally in the A/FDs.
f. EFAS is not intended to be used for filing or
closing flight plans, position reporting, getting
complete preflight briefings, or obtaining random
weather reports and forecasts. En route flight
advisories are tailored to the phase of flight that
begins after climb-out and ends with descent to land.
Immediate destination weather and terminal aerodrome forecasts will be provided on request. Pilots
requesting information not within the scope of flight
watch will be advised of the appropriate AFSS/FSS
frequency to obtain the information. Pilot participation is essential to the success of EFAS by providing
a continuous exchange of information on weather,
winds, turbulence, flight visibility, icing, etc.,
between pilots and flight watch specialists. Pilots are
encouraged to report good weather as well as bad, and
to confirm expected conditions as well as unexpected
to EFAS facilities.
7-1-6. Inflight Aviation Weather Advisories
a. Background
1. Inflight Aviation Weather Advisories are
forecasts to advise en route aircraft of development of
potentially hazardous weather. All inflight aviation
weather advisories in the conterminous U.S. are
issued by the Aviation Weather Center (AWC) in
Kansas City, Missouri. The Weather Forecast
Office (WFO) in Honolulu issues advisories for the
Hawaiian Islands. In Alaska, the Alaska Aviation
Weather Unit (AAWU) issues inflight aviation
weather advisories. All heights are referenced MSL,
except in the case of ceilings (CIG) which indicate
AGL.
2. There are three types of inflight aviation
weather advisories: the Significant Meteorological
Information (SIGMET), the Convective SIGMET
and the Airmen's Meteorological Information
(AIRMET). All of these advisories use the same
location identifiers (either VORs, airports, or
well-known geographic areas) to describe the
hazardous weather areas. See
FIG 7-1-3 and
FIG 7-1-4. Graphics with improved clarity can be
found in Advisory Circular AC 00-45E, Aviation
Weather Services, which is available on the following
web site: http://www.faa.gov.
3. Two other weather products supplement
these Inflight Aviation Weather Advisories:
(a) The Severe Weather Watch Bulletins (WWs), (with associated Alert Messages)
(AWW), and
(b) The Center Weather Advisories (CWAs).
FIG 7-1-2
EFAS Radio Coverage Areas
NOTE-
EFAS radio coverage at 5000 feet AGL. The shaded areas depict limited coverage areas in which altitudes above 5000 feet
AGL would be required to contact EFAS.
FIG 7-1-3
Inflight Advisory Plotting Chart
FIG 7-1-4
Geographical Areas and Terrain Features
FIG 7-1-5
Aviation Area Forecasts
FA Locations - Contiguous United States
b. SIGMET (WS)/AIRMET (WA)
SIGMETs/AIRMETs are issued corresponding to the
Area Forecast (FA) areas described in
FIG 7-1-5,
FIG 7-1-6 and
FIG 7-1-7. The maximum forecast
period is 4 hours for SIGMETs and 6 hours for
AIRMETs. Both advisories are considered "widespread" because they must be either affecting or be
forecasted to affect an area of at least 3,000 square
miles at any one time. However, if the total area to be
affected during the forecast period is very large, it
could be that in actuality only a small portion of this
total area would be affected at any one time.
FIG 7-1-6
Alaska Area Forecast Sectors
FIG 7-1-7
Hawaii Area Forecast Locations
c. SIGMET (WS)
1. A SIGMET advises of nonconvective
weather that is potentially hazardous to all aircraft.
SIGMETs are unscheduled products that are valid for
4 hours. However, conditions that are associated with
hurricanes are valid for 6 hours. Unscheduled updates
and corrections are issued as necessary. In the
conterminous U.S., SIGMETs are issued when the
following phenomena occur or are expected to occur:
(a) Severe icing not associated with thunderstorms.
(b) Severe or extreme turbulence or clear air
turbulence (CAT) not associated with thunderstorms.
(c) Dust storms or sandstorms lowering
surface or inflight visibilities to below 3 miles.
(d) Volcanic ash.
2. In Alaska and Hawaii, SIGMETs are also
issued for:
(a) Tornadoes.
(b) Lines of thunderstorms.
(c) Embedded thunderstorms.
(d) Hail greater than or equal to 3/4 inch in
diameter.
3. SIGMETs are identified by an alphabetic
designator from November through Yankee excluding Sierra and Tango. (Sierra, Tango, and Zulu are
reserved for AIRMETs.) The first issuance of a
SIGMET will be labeled as UWS (Urgent Weather
SIGMET). Subsequent issuances are at the forecaster's discretion. Issuance for the same phenomenon
will be sequentially numbered, using the original
designator until the phenomenon ends. For example,
the first issuance in the Chicago (CHI) FA area for
phenomenon moving from the Salt Lake City (SLC)
FA area will be SIGMET Papa 3, if the previous two
issuances, Papa 1 and Papa 2, had been in the SLC FA
area. Note that no two different phenomena across the
country can have the same alphabetic designator at
the same time.
EXAMPLE-
Example of a SIGMET:
BOSR WS 050600
SIGMET ROMEO 2 VALID UNTIL 051000
ME NH VT
FROM CAR TO YSJ TO CON TO MPV TO CAR
MOD TO OCNL SEV TURB BLW 080 EXP DUE TO STG
NWLY FLOW. CONDS CONTG BYD
1000Z.
d. Convective SIGMET (WST)
1. Convective SIGMETs are issued in the
conterminous U.S. for any of the following:
(a) Severe thunderstorm due to:
(1) Surface winds greater than or equal to
50 knots.
(2) Hail at the surface greater than or equal
to 3/4 inches in diameter.
(3) Tornadoes.
(b) Embedded thunderstorms.
(c) A line of thunderstorms.
(d) Thunderstorms producing precipitation
greater than or equal to heavy precipitation affecting
40 percent or more of an area at least 3,000 square
miles.
2. Any convective SIGMET implies severe or
greater turbulence, severe icing, and low-level wind
shear. A convective SIGMET may be issued for any
convective situation that the forecaster feels is
hazardous to all categories of aircraft.
3. Convective SIGMET bulletins are issued for
the western (W), central (C), and eastern (E) United
States. (Convective SIGMETs are not issued for
Alaska or Hawaii.) The areas are separated at 87 and
107 degrees west longitude with sufficient overlap to
cover most cases when the phenomenon crosses the
boundaries. Bulletins are issued hourly at H+55.
Special bulletins are issued at any time as required
and updated at H+55. If no criteria meeting
convective SIGMET requirements are observed or
forecasted, the message "CONVECTIVE SIGMET...
NONE" will be issued for each area at H+55.
Individual convective SIGMETs for each area (W, C,
E) are numbered sequentially from number one each
day, beginning at 00Z. A convective SIGMET for a
continuing phenomenon will be reissued every hour
at H+55 with a new number. The text of the bulletin
consists of either an observation and a forecast or just
a forecast. The forecast is valid for up to 2 hours.
EXAMPLE-
Example of a Convective SIGMET:
MKCC WST 251655
CONVECTIVE SIGMET 54C
VALID UNTIL 1855Z
WI IL
FROM 30E MSN-40ESE DBQ
DMSHG LINE TS 15 NM WIDE MOV FROM 30025KT.
TOPS TO FL450. WIND GUSTS TO 50 KT POSS.
CONVECTIVE SIGMET 55C
VALID UNTIL 1855Z
WI IA
FROM 30NNW MSN-30SSE MCW
DVLPG LINE TS 10 NM WIDE MOV FROM 30015KT.
TOPS TO FL300.
CONVECTIVE SIGMET 56C
VALID UNTIL 1855Z
MT ND SD MN IA MI
LINE TS 15 NM WIDE MOV FROM 27020KT. TOPS TO
FL380.
OUTLOOK VALID 151855-252255
FROM 60NW ISN-INL-TVC-SBN-BRL-FSD-BIL-60NW ISN
IR STLT IMGRY SHOWS CNVTV CLD TOP TEMPS
OVER SRN WI HAVE BEEN WARMING STEADILY
INDCG A WKNG TREND. THIS ALSO REFLECTED BY
LTST RADAR AND LTNG DATA. WKNG TREND OF
PRESENT LN MAY CONT...HWVR NEW DVLPMT IS
PSBL ALG OUTFLOW BDRY AND/OR OVR NE IA/SW
WI BHD CURRENT ACT.
A SCND TS IS CONTG TO MOV EWD THRU ERN MT
WITH NEW DVLPMT OCRG OVR CNTRL ND. MT ACT
IS MOVG TWD MORE FVRBL AMS OVR THE WRN
DAKS WHERE DWPTS ARE IN THE UPR 60S WITH
LIFTED INDEX VALUES TO MS 6. TS EXPD TO INCR IN
COVERAGE AND INTSTY DURG AFTN HRS.
WST ISSUANCES EXPD TO BE RQRD THRUT AFTN
HRS WITH INCRG PTNTL FOR STGR CELLS TO
CONTAIN LRG HAIL AND PSBLY DMGG SFC WNDS.
e. International SIGMET
1. Some NWS offices have been designated by
the ICAO as Meteorological Watch Offices (MWOs).
These offices are responsible for issuing International
SIGMETs for designated areas that include Alaska,
Hawaii, portions of the Atlantic and Pacific Oceans,
and the Gulf of Mexico.
2. The offices which issue International
SIGMETs are:
(a) The AWC in Kansas City, Missouri.
(b) The AAWU in Anchorage, Alaska.
(c) The WFO in Honolulu, Hawaii.
(d) The WFO on Guam Island in the Pacific
Ocean.
3. These SIGMETs are considered "widespread" because they must be either affecting or be
forecasted to affect an area of at least 3,000 square
miles at any one time. The International SIGMET is
issued for 12 hours for volcanic ash events, 6 hours
for hurricanes and tropical storms, and 4 hours for all
other events. Like the domestic SIGMETs, International SIGMETs are also identified by an alphabetic
designator from Alpha through Mike and are
numbered sequentially until that weather phenomenon ends. The criteria for an International SIGMET
are:
(a) Thunderstorms occurring in lines, embedded in clouds, or in large areas producing
tornadoes or large hail.
(b) Tropical cyclones.
(c) Severe icing.
(d) Severe or extreme turbulence.
(e) Dust storms and sandstorms lowering
visibilities to less than 3 miles.
(f) Volcanic ash.
EXAMPLE-
Example of an International SIGMET:
WSNT06 KKCI 022014
SIGA0F
KZMA KZNY TJZS SIGMET FOXTROT 3 VALID
022015/030015 KKCI- MIAMI OCEANIC FIR NEW
YORK OCEANIC FIR SAN JUAN FIR FRQ TS WI AREA
BOUNDED BY 2711N6807W 2156N6654W 2220N7040W
2602N7208W 2711N6807W. TOPS TO FL470. MOV NE
15KT. WKN. BASED ON SAT AND LTG OBS.
MOSHER
f. AIRMET (WA)
1. AIRMETs (WAs) are advisories of significant weather phenomena but describe conditions at
intensities lower than those which require the
issuance of SIGMETs. AIRMETs are intended for
dissemination to all pilots in the preflight and en route
phase of flight to enhance safety. AIRMET Bulletins
are issued on a scheduled basis every 6 hours
beginning at 0145 UTC during Central Daylight
Time and at 0245 UTC during Central Standard Time.
Unscheduled updates and corrections are issued as
necessary. Each AIRMET Bulletin contains any
current AIRMETs in effect and an outlook for
conditions expected after the AIRMET valid period.
AIRMETs contain details about IFR, extensive
mountain obscuration, turbulence, strong surface
winds, icing, and freezing levels.
2. There are three AIRMETs: Sierra, Tango,
and Zulu. After the first issuance each day, scheduled
or unscheduled bulletins are numbered sequentially
for easier identification.
(a) AIRMET Sierra describes IFR conditions
and/or extensive mountain obscurations.
(b) AIRMET Tango describes moderate
turbulence, sustained surface winds of 30 knots or
greater, and/or nonconvective low-level wind shear.
(c) AIRMET Zulu describes moderate icing
and provides freezing level heights.
EXAMPLE-
Example of AIRMET Sierra issued for the Chicago FA
area:
CHIS WA 121345
AIRMET SIERRA UPDT 3 FOR IFR AND MTN OBSCN
VALID UNTIL 122000.
AIRMET IFR...SD NE MN IA MO WI LM MI IL IN KY
FROM 70NW RAP TO 50W RWF TO 50W MSN TO GRB
TO MBS TO FWA TO CVG TO HNN TO TRI TO ARG TO
40SSW BRL TO OMA TO BFF TO 70NW RAP
OCNL CIG BLW 010/VIS BLW 3SM FG/BR. CONDS
ENDG 15Z-17Z.
AIRMET MTN OBSCN...KY TN
FROM HNN TO TRI TO CHA TO LOZ TO HNN
MTNS OCNL OBSC CLDS/PCPN/BR. CONDS ENDG TN
PTN AREA 18Z- 20Z..CONTG KY BYD 20Z..ENDG 02Z.
EXAMPLE-
Example of AIRMET Tango issued for the Salt Lake City
FA area:
SLCT WA 121345
AIRMET TANGO UPDT 2 FOR TURB VALID UNTIL
122000.
AIRMET TURB...NV UT CO AZ NM
FROM LKV TO CHE TO ELP TO 60S TUS TO YUM TO
EED TO RNO TO LKV OCNL MOD TURB BLW FL180
DUE TO MOD SWLY/WLY WNDS. CONDS CONTG BYD
20Z THRU 02Z.
AIRMET TURB...NV WA OR CA CSTL WTRS
FROM BLI TO REO TO BTY TO DAG TO SBA TO 120W
FOT TO 120W TOU TO BLI
OCNL MOD TURB BTWN FL180 AND FL400 DUE TO
WNDSHR ASSOCD WITH JTSTR. CONDS CONTG BYD
20Z THRU 02Z.
EXAMPLE-
Example of AIRMET Zulu issued for the San Francisco
FA area:
SFOZ WA 121345
AIRMET ZULU UPDT 2 FOR ICE AND FRZLVL VALID
UNTIL 122000.
AIRMET ICE...WA OR ID MT NV UT
FROM YQL TO SLC TO WMC TO LKV TO PDT TO YDC
TO YQL
LGT OCNL MOD RIME/MXD ICGICIP BTWN FRZLVL
AND FL220. FRZLVL 080-120. CONDS CONTG BYD
20Z THRU 02Z.
AIRMET ICE...WA OR
FROM YDC TO PDT TO LKV TO 80W MFR TO ONP TO
TOU TO YDC
LGT OCNL MOD RIME/MXD ICGICIP BTWN FRZLVL
AND FL180. FRZLVL 060-080. CONDS CONTG BYD
20Z THRU 02Z.
FRZLVL...WA...060 CSTLN SLPG 100 XTRM E.
OR...060-070 CASCDS WWD. 070-095 RMNDR.
NRN CA...060-100 N OF A 30N FOT-40N RNO LN SLPG
100-110 RMNDR.
g. Severe Weather Watch Bulletins (WWs) and
Alert Messages (AWWs)
1. WWs define areas of possible severe
thunderstorms or tornado activity. The bulletins are
issued by the Storm Prediction Center (SPC) in
Norman, OK. WWs are unscheduled and are issued
as required.
2. A severe thunderstorm watch describes areas
of expected severe thunderstorms. (Severe thunderstorm criteria are 3/4-inch hail or larger and/or wind
gusts of 50 knots [58 mph] or greater.)
3. A tornado watch describes areas where the
threat of tornadoes exists.
4. In order to alert the WFOs, CWSUs, FSSs,
and other users, a preliminary notification of a watch
called the Alert Severe Weather Watch bulletin
(AWW) is sent before the WW. (WFOs know this
product as a SAW).
EXAMPLE-
Example of an AWW:
MKC AWW 011734
WW 75 TORNADO TX OK AR 011800Z-020000Z
AXIS..80 STATUTE MILES EAST AND WEST OF A
LINE..60ESE DAL/DALLAS TX/ - 30 NW ARG/ WALNUT
RIDGE AR/
..AVIATION COORDS.. 70NM E/W /58W GGG - 25NW
ARG/
HAIL SURFACE AND ALOFT..1 3/4 INCHES. WIND
GUSTS..70 KNOTS. MAX TOPS TO 450. MEAN WIND
VECTOR 24045.
5. Soon after the AWW goes out, the actual
watch bulletin itself is issued. A WW is in the
following format:
(a) Type of severe weather watch, watch area,
valid time period, type of severe weather possible,
watch axis, meaning of a watch, and a statement that
persons should be on the lookout for severe weather.
(b) Other watch information; i.e., references
to previous watches.
(c) Phenomena, intensities, hail size, wind
speed (knots), maximum cumulonimbus (CB) tops,
and estimated cell movement (mean wind vector).
(d) Cause of severe weather.
(e) Information on updating Convective
Outlook (AC) products.
EXAMPLE-
Example of a WW:
BULLETIN - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 381
STORM PREDICTION CENTER NORMAN OK
556 PM CDT MON JUN 2 1997
THE STORM PREDICTON CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF NORTHEAST
NEW MEXICO TEXAS PANHANDLE
EFFECTIVE THIS MONDAY NIGHT AND TUESDAY
MORNING FROM 630 PM UNTIL MIDNIGHT CDT.
TORNADOES...HAIL TO 2 3/4 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE
IN THESE AREAS.
THE TORNADO WATCH AREA IS ALONG AND 60
STATUTE MILES NORTH AND SOUTH OF A LINE
FROM 50 MILES SOUTHWEST OF RATON NEW
MEXICO TO 50 MILES EAST OF AMARILLO TEXAS.
REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR TORNADOES AND
SEVERE THUNDERSTORMS IN AND CLOSE TO THE
WATCH AREA. PERSONS IN THESE AREAS SHOULD
BE ON THE LOOKOUT FOR THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER
STATEMENTS AND POSSIBLE WARNINGS.
OTHER WATCH INFORMATION...CONTINUE...
WW 378...WW 379...WW 380
DISCUSSION...THUNDERSTORMS ARE INCREASING
OVER NE NM IN MOIST SOUTHEASTERLY UPSLOPE
FLOW. OUTFLOW BOUNDARY EXTENDS EASTWARD
INTO THE TEXAS PANHANDLE AND EXPECT STORMS
TO MOVE ESE ALONG AND NORTH OF THE
BOUNDARY ON THE N EDGE OF THE CAP. VEERING
WINDS WITH HEIGHT ALONG WITH INCREASGING
MID LVL FLOW INDICATE A THREAT FOR SUPERCELLS.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 2
3/4 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 70 KNOTS. A FEW CUMULONIMBI
WITH MAXIMUM TOPS TO 550. MEAN STORM
MOTION VECTOR 28025.
6. Status reports are issued as needed to show
progress of storms and to delineate areas no longer
under the threat of severe storm activity. Cancellation
bulletins are issued when it becomes evident that no
severe weather will develop or that storms have
subsided and are no longer severe.
7. When tornadoes or severe thunderstorms
have developed, the local WFO office will issue the
warnings covering those areas.
h. Center Weather Advisories (CWAs)
1. CWAs are unscheduled inflight, flow control,
air traffic, and air crew advisory. By nature of its short
lead time, the CWA is not a flight planning product.
It is generally a nowcast for conditions beginning
within the next two hours. CWAs will be issued:
(a) As a supplement to an existing SIGMET,
Convective SIGMET or AIRMET.
(b) When an Inflight Advisory has not been
issued but observed or expected weather conditions
meet SIGMET/AIRMET criteria based on current
pilot reports and reinforced by other sources
of information about existing meteorological
conditions.
(c) When observed or developing weather
conditions do not meet SIGMET, Convective
SIGMET, or AIRMET criteria; e.g., in terms of
intensity or area coverage, but current pilot reports or
other weather information sources indicate that
existing or anticipated meteorological phenomena
will adversely affect the safe flow of air traffic within
the ARTCC area of responsibility.
2. The following example is a CWA issued from
the Kansas City, Missouri, ARTCC. The "3" after
ZKC in the first line denotes this CWA has been
issued for the third weather phenomena to occur for
the day. The "301" in the second line denotes the
phenomena number again (3) and the issuance
number (01) for this phenomena. The CWA was
issued at 2140Z and is valid until 2340Z.
EXAMPLE-
ZKC3 CWA 032140
ZKC CWA 301 VALID UNTIL 032340
ISOLD SVR TSTM over KCOU MOVG SWWD
10 KTS ETC.
7-1-7. Categorical Outlooks
a. Categorical outlook terms, describing general
ceiling and visibility conditions for advanced
planning purposes are used only in area forecasts and
are defined as follows:
1. LIFR (Low IFR). Ceiling less than 500 feet
and/or visibility less than 1 mile.
2. IFR. Ceiling 500 to less than 1,000 feet
and/or visibility 1 to less than 3 miles.
3. MVFR (Marginal VFR). Ceiling 1,000 to
3,000 feet and/or visibility 3 to 5 miles inclusive.
4. VFR. Ceiling greater than 3,000 feet and
visibility greater than 5 miles; includes sky clear.
b. The cause of LIFR, IFR, or MVFR is indicated
by either ceiling or visibility restrictions or both. The
contraction "CIG" and/or weather and obstruction to
vision symbols are used. If winds or gusts of 25 knots
or greater are forecast for the outlook period, the word
"WIND" is also included for all categories including
VFR.
EXAMPLE-
1. LIFR CIG-low IFR due to low ceiling.
2. IFR FG-IFR due to visibility restricted by fog.
3. MVFR CIG HZ FU-marginal VFR due to both ceiling
and visibility restricted by haze and smoke.
4. IFR CIG RA WIND-IFR due to both low ceiling and
visibility restricted by rain; wind expected to be 25 knots or
greater.
7-1-8. Telephone Information Briefing
Service (TIBS)
a. TIBS, provided by automated flight service
stations (AFSSs) is a continuous recording of
meteorological and aeronautical information, available by telephone. Each AFSS provides at least four
route and/or area briefings. In addition, airspace
procedures and special announcements (if applicable) concerning aviation interests may also be
available. Depending on user demand, other items
may be provided; i.e., METAR observations,
terminal aerodrome forecasts, wind/temperatures
aloft forecasts, etc.
b. TIBS is not intended to substitute for
specialist-provided preflight briefings. It is, however,
recommended for use as a preliminary briefing, and
often will be valuable in helping you to make a "go or
no go" decision.
c. TIBS is provided by Automated Flight Service
Stations (AFSSs) and provides continuous telephone
recordings of meteorological and/or aeronautical
information. Specifically, TIBS provides area and/or
route briefings, airspace procedures, and special
announcements (if applicable) concerning aviation
interests.
d. Depending on user demand, other items may be
provided; i.e., surface observations, terminal forecasts, winds/temperatures aloft forecasts, etc. A
TOUCH-TONE™ telephone is necessary to fully
utilize the TIBS program.
e. Pilots are encouraged to avail themselves of this
service. TIBS locations are found at AFSS sites and
can be accessed by use of 1-800-WX BRIEF toll free
number.
7-1-9. Transcribed Weather Broadcast
(TWEB) (Alaska Only)
Equipment is provided in Alaska by which
meteorological and aeronautical data are recorded on
tapes and broadcast continuously over selected L/MF
and VOR facilities. Broadcasts are made from a series
of individual tape recordings, and changes, as they
occur, are transcribed onto the tapes. The information
provided varies depending on the type equipment
available. Generally, the broadcast contains a
summary of adverse conditions, surface weather
observations, pilot weather reports, and a density
altitude statement (if applicable). At the discretion of
the broadcast facility, recordings may also include a
synopsis, winds aloft forecast, en route and terminal
forecast data, and radar reports. At selected locations,
telephone access to the TWEB has been provided
(TEL-TWEB). Telephone numbers for this service
are found in the Supplement Alaska A/FD. These
broadcasts are made available primarily for preflight
and inflight planning, and as such, should not be
considered as a substitute for specialist-provided
preflight briefings.
7-1-10. Inflight Weather Broadcasts
a. Weather Advisory Broadcasts. ARTCCs
broadcast a Severe Weather Forecast Alert (AWW),
Convective SIGMET, SIGMET, or CWA alert once
on all frequencies, except emergency, when any part
of the area described is within 150 miles of the
airspace under their jurisdiction. These broadcasts
contain SIGMET or CWA (identification) and a brief
description of the weather activity and general area
affected.
EXAMPLE-
1. Attention all aircraft, SIGMET Delta Three, from Myton
to Tuba City to Milford, severe turbulence and severe clear
icing below one zero thousand feet. Expected to continue
beyond zero three zero zero zulu.
2. Attention all aircraft, convective SIGMET Two Seven
Eastern. From the vicinity of Elmira to Phillipsburg.
Scattered embedded thunderstorms moving east at one
zero knots. A few intense level five cells, maximum tops four
five zero.
3. Attention all aircraft, Kansas City Center weather
advisory one zero three. Numerous reports of moderate to
severe icing from eight to niner thousand feet in a three zero
mile radius of St. Louis. Light or negative icing reported
from four thousand to one two thousand feet remainder of
Kansas City Center area.
NOTE-
Terminal control facilities have the option to limit the
AWW, convective SIGMET, SIGMET, or CWA broadcast as
follows: local control and approach control positions may
opt to broadcast SIGMET or CWA alerts only when any
part of the area described is within 50 miles of the airspace
under their jurisdiction.
b. Hazardous Inflight Weather Advisory Service (HIWAS). This is a continuous broadcast of
inflight weather advisories including summarized
AWW, SIGMETs, Convective SIGMETs, CWAs,
AIRMETs, and urgent PIREPs. HIWAS has been
adopted as a national program and will be
implemented throughout the conterminous U.S. as
resources permit. In those areas where HIWAS is
commissioned, ARTCC, Terminal ATC, and AFSS/FSS facilities have discontinued the broadcast of
inflight advisories as described in the preceding
paragraph. HIWAS is an additional source of
hazardous weather information which makes these
data available on a continuous basis. It is not,
however, a replacement for preflight or inflight
briefings or real-time weather updates from Flight
Watch (EFAS). As HIWAS is implemented in
individual center areas, the commissioning will be
advertised in the Notices to Airmen Publication.
1. Where HIWAS has been implemented, a
HIWAS alert will be broadcast on all except
emergency frequencies once upon receipt by ARTCC
and terminal facilities, which will include an alert
announcement, frequency instruction, number, and
type of advisory updated; e.g., AWW, SIGMET,
Convective SIGMET, or CWA.
EXAMPLE-
Attention all aircraft. Hazardous weather information
(SIGMET, Convective SIGMET, AIRMET, Urgent Pilot
Weather Report (UUA), or Center Weather Advisory
(CWA), Number or Numbers) for (geographical area)
available on HIWAS, Flight Watch, or Flight Service
frequencies.
2. In HIWAS ARTCC areas, AFSS/FSSs will
broadcast a HIWAS update announcement once on all
except emergency frequencies upon completion of
recording an update to the HIWAS broadcast.
Included in the broadcast will be the type of advisory
updated; e.g., AWW, SIGMET, Convective
SIGMET, CWA, etc.
EXAMPLE-
Attention all aircraft. Hazardous weather information for
(geographical area) available from Flight Watch or Flight
Service.
3. HIWAS availability is shown on IFR Enroute
Low Altitude Charts and VFR Sectional Charts. The
symbol depiction is identified in the chart legend.
7-1-11. Flight Information Services (FIS)
a. FIS. Aviation weather and other operational
information may be displayed in the cockpit through
the use of FIS. FIS systems are of two basic types:
Broadcast only systems (called FIS-B) and two-way
request/reply systems. Broadcast system components
include a ground- or space-based transmitter, an
aircraft receiver, and a portable or installed cockpit
display device. Two-way systems utilize transmitter/receivers at both the ground- or space-based site and
the aircraft.
1. Broadcast FIS (i.e., FIS-B) allows the pilot to
passively collect weather and other operational data
and to display that data at the appropriate time. In
addition to textual weather products such as Aviation
Routine Weather Reports (METARs)/ Aviation
Selected Special Weather Reports (SPECIs) and
Terminal Area Forecasts (TAFs), graphical weather
products such as radar composite/mosaic images,
temporary flight restricted airspace and other
NOTAMs may be provided to the cockpit. Two-way
FIS services permit the pilot to make specific weather
and other operational information requests for
cockpit display. A FIS service provider will then
prepare a reply in response to that specific request and
transmit the product to that specific aircraft.
2. FIS services are available from four types of
service providers:
(a) A private sector FIS provider operating
under service agreement with the FAA using
broadcast data link over VHF aeronautical spectrum
and whose products have been reviewed and accepted
by the FAA prior to transmission. (Products and
services are defined under subparagraph
c.)
(b) Through an FAA operated service using a
broadcast data link on the ADS-B UAT network.
(Products and services are defined under subparagraph
d.)
(c) Private sector FIS providers operating
under customer contracts using aeronautical spectrum.
(d) Private sector FIS providers operating
under customer contract using methods other than
aeronautical spectrum, including Internet data-to-the-cockpit service providers.
3. FIS is a method of receiving aviation weather
and other operational data in the cockpit that
augments traditional pilot voice communication with
FAA's Flight Service Stations (FSSs), ATC facilities,
or Airline Operations Control Centers (AOCCs). FIS
is not intended to replace traditional pilot and
controller/flight service specialist/aircraft dispatcher
pre-flight briefings or inflight voice communications. FIS; however, can provide textual and
graphical background information that can help
abbreviate and improve the usefulness of such
communications. FIS enhances pilot situational
awareness and improves safety.
4. To ensure airman compliance with Federal
Aviation Regulations, manufacturer's operating
manuals should remind airmen to contact ATC
controllers, FSS specialists, operator dispatchers, or
airline operations control centers for general and
mission critical aviation weather information and/or
NAS status conditions (such as NOTAMs, Special
Use Airspace status, and other government flight
information). If FIS products are systemically
modified (for example, are displayed as abbreviated
plain text and/or graphical depictions), the modification process and limitations of the resultant product
should be clearly described in the vendor's user
guidance.
b. Operational Use of FIS. Regardless of the
type of FIS system being used, several factors must
be considered when using FIS:
1. Before using FIS for inflight operations,
pilots and other flight crewmembers should become
familiar with the operation of the FIS system to be
used, the airborne equipment to be used, including its
system architecture, airborne system components,
coverage service volume and other limitations of the
particular system, modes of operation and indications
of various system failures. Users should also be
familiar with the specific content and format of the
services available from the FIS provider(s). Sources
of information that may provide this specific
guidance include manufacturer's manuals, training
programs and reference guides.
2. FIS should not serve as the sole source of
aviation weather and other operational information.
ATC, AFSSs and, if applicable, AOCC VHF/HF
voice remain as a redundant method of communicating aviation weather, NOTAMs, and other
operational information to aircraft in flight. FIS
augments these traditional ATC/FSS/AOCC services
and, for some products, offers the advantage of being
displayed as graphical information. By using FIS for
orientation, the usefulness of information received
from conventional means may be enhanced. For
example, FIS may alert the pilot to specific areas of
concern that will more accurately focus requests
made to FSS or AOCC for inflight updates or similar
queries made to ATC.
3. The airspace and aeronautical environment is
constantly changing. These changes occur quickly
and without warning. Critical operational decisions
should be based on use of the most current and
appropriate data available. When differences exist
between FIS and information obtained by voice
communication with ATC, FSS, and/or AOCC (if
applicable), pilots are cautioned to use the most
recent data from the most authoritative source.
4. FIS aviation weather products (e.g., graphical
ground-based radar precipitation depictions) are not
appropriate for tactical avoidance of severe weather
such as negotiating a path through a weather hazard
area. FIS supports strategic weather decision making
such as route selection to avoid a weather hazard area
in its entirety. The misuse of information beyond its
applicability may place the pilot and aircraft in
jeopardy. In addition, FIS should never be used in lieu
of an individual pre-flight weather and flight
planning briefing.
5. FIS NOTAM products, including Temporary
Flight Restriction (TFR) information, are advisory-use information and are intended for situational
awareness purposes only. Cockpit displays of this
information are not appropriate for tactical navigation - pilots should stay clear of any geographic area
displayed as a TFR NOTAM. Pilots should contact
FSSs and/or ATC while en route to obtain updated
information and to verify the cockpit display of
NOTAM information.
6. FIS supports better pilot decision making by
increasing situational awareness. Better decision-making is based on using information from a variety
of sources. In addition to FIS, pilots should take
advantage of other weather/NAS status sources,
including, briefings from Flight Service Stations,
FAA's en route "Flight Watch" service, data from
other air traffic control facilities, airline operation
control centers, pilot reports, as well as their own
observations.
c. FAA FISDL (VHF) Service. The FAA's
FISDL (VHF datalink) system is a VHF Data Link
(VDL) Mode 2 implementation that provides pilots
and flight crews of properly equipped aircraft with a
cockpit display of certain aviation weather and flight
operational information. This information may be
displayed in both textual and graphical formats. The
system is operated under a service agreement with the
FAA, using broadcast data link on VHF aeronautical
spectrum on two 25 KHz spaced frequencies
(136.450 and 136.475 MHz). The FAA FISDL
(VHF) service is designed to provide coverage
throughout the continental U.S. from 5,000 feet AGL
to 17,500 feet MSL, except in areas where this is not
feasible due to mountainous terrain. Aircraft
operating near transmitter sites may receive useable
FISDL signals at altitudes lower than 5,000 feet
AGL, including on the surface in some locations,
depending on transmitter/aircraft line of sight
geometry. Aircraft operating above 17,500 feet MSL
may also receive useable FISDL signals under certain
circumstances.
1. FAA FISDL (VHF) service provides, free of
charge, the following basic text products:
(a) Aviation Routine Weather Reports
(METARs).
(b) Aviation Selected Special Weather
Reports (SPECIs).
(c) Terminal Area Forecasts (TAFs), and their
amendments.
(d) Significant Meteorological Information
(SIGMETs).
(e) Convective SIGMETs.
(f) Airman's Meteorological Information
(AIRMETs).
(g) Pilot Reports (both urgent and routine)
(PIREPs); and,
(h) Severe Weather Forecast Alerts and
Warnings (AWWs/WW) issued by the NOAA Storm
Prediction Center (SPC).
2. The format and coding of these text products
are described in Advisory Circular AC-00-45,
Aviation Weather Services, and paragraph
7-1-30,
Key to Aerodrome Forecast (TAF) and Aviation
Routine Weather Report (METAR).
3. Additional products, called "Value-Added
Products," are also available from the vendor on a
paid subscription basis. Details concerning the
content, format, symbology and cost of these
products may be obtained from the vendor.
d. FAA's Flight Information Service-Broadcast (FIS-B) Service. FIS-B is a ground broadcast
service provided through the FAA's Universal Access
Transceiver (UAT) "ADS-B Broadcast Services"
network. The UAT network is an ADS-B data link
that operates on 978 MHz. The FAA FIS-B system
provides pilots and flight crews of properly equipped
aircraft with a cockpit display of certain aviation
weather and flight operational information. The
FAA's FIS-B service is being introduced in certain
regional implementations within the NAS (e.g., in
Alaska and in other areas of implementation).
1. FAA's UAT FIS-B provides the initial
products listed below with additional products
planned for future implementation. FIS-B reception
is line of sight and can be expected within 200 NM
(nominal range) of each ground transmitting site. The
following services are provided free of charge.
(a) Text: Aviation Routine Weather Reports
(METARs).
(b) Text: Special Aviation Reports
(SPECIs).
(c) Text: Terminal Area Forecasts (TAFs),
and their amendments.
(d) Graphic: NEXRAD precipitation maps.
2. The format and coding of the above text
weather-related products are described in Advisory
Circular AC-00-45, Aviation Weather Services, and
paragraph
7-1-30, Key to Aerodrome Forecast
(TAF) and Aviation Routine Weather Report
(METAR).
3. Details concerning the content, format, and
symbology of the various data link products provided
may be obtained from the specific avionics
manufacturer.
e. Non-FAA FISDL Systems. Several commercial vendors also provide customers with FIS data
over both the aeronautical spectrum and on other
frequencies using a variety of data link protocols. In
some cases, the vendors provide only the communications system that carries customer messages,
such as the Aircraft Communications Addressing and
Reporting System (ACARS) used by many air carrier
and other operators.
1. Operators using non-FAA FIS data for
inflight weather and other operational information
should ensure that the products used conform to
FAA/NWS standards. Specifically, aviation weather
and NAS status information should meet the
following criteria:
(a) The products should be either FAA/NWS
"accepted" aviation weather reports or products, or
based on FAA/NWS accepted aviation weather
reports or products. If products are used which do not
meet this criteria, they should be so identified. The
operator must determine the applicability of such
products to their particular flight operations.
(b) In the case of a weather product which is
the result of the application of a process which alters
the form, function or content of the base FAA/NWS
accepted weather product(s), that process, and any
limitations to the application of the resultant product,
should be described in the vendor's user guidance
material.
2. An example would be a NEXRAD radar
composite/mosaic map, which has been modified by
changing the scaling resolution. The methodology of
assigning reflectivity values to the resultant image
components should be described in the vendor's
guidance material to ensure that the user can
accurately interpret the displayed data.
7-1-12. Weather Observing Programs
a. Manual Observations. With only a few
exceptions, these reports are from airport locations
staffed by FAA or NWS personnel who manually
observe, perform calculations, and enter these
observations into the (WMSCR) communication
system. The format and coding of these observations
are contained in paragraph
7-1-30, Key to Aviation
Routine Weather Report (METAR) and Aerodrome
Forecasts (TAF).
b. Automated Weather Observing System
(AWOS).
1. Automated weather reporting systems are
increasingly being installed at airports. These
systems consist of various sensors, a processor, a
computer-generated voice subsystem, and a transmitter to broadcast local, minute-by-minute weather data
directly to the pilot.
NOTE-
When the barometric pressure exceeds 31.00 inches Hg.,
see paragraph
7-2-2, Procedures, for the
altimeter setting procedures.
2. The AWOS observations will include the
prefix "AUTO" to indicate that the data are derived
from an automated system. Some AWOS locations
will be augmented by certified observers who will
provide weather and obstruction to vision information in the remarks of the report when the reported
visibility is less than 7 miles. These sites, along with
the hours of augmentation, are to be published in the
A/FD. Augmentation is identified in the observation
as "OBSERVER WEATHER." The AWOS wind
speed, direction and gusts, temperature, dew point,
and altimeter setting are exactly the same as for
manual observations. The AWOS will also report
density altitude when it exceeds the field elevation by
more than 1,000 feet. The reported visibility is
derived from a sensor near the touchdown of the
primary instrument runway. The visibility sensor
output is converted to a visibility value using a
10-minute harmonic average. The reported sky
condition/ceiling is derived from the ceilometer
located next to the visibility sensor. The AWOS
algorithm integrates the last 30 minutes of ceilometer
data to derive cloud layers and heights. This output
may also differ from the observer sky condition in
that the AWOS is totally dependent upon the cloud
advection over the sensor site.
3. These real-time systems are operationally
classified into four basic levels:
(a) AWOS-A only reports altimeter setting;
NOTE-
Any other information is advisory only.
(b) AWOS-l usually reports altimeter setting, wind data, temperature, dew point, and density
altitude;
(c) AWOS-2 provides the information provided by AWOS-l plus visibility; and
(d) AWOS-3 provides the information provided by AWOS-2 plus cloud/ceiling data.
4. The information is transmitted over a discrete
VHF radio frequency or the voice portion of a local
NAVAID. AWOS transmissions on a discrete VHF
radio frequency are engineered to be receivable to a
maximum of 25 NM from the AWOS site and a
maximum altitude of 10,000 feet AGL. At many
locations, AWOS signals may be received on the
surface of the airport, but local conditions may limit
the maximum AWOS reception distance and/or
altitude. The system transmits a 20 to 30 second
weather message updated each minute. Pilots should
monitor the designated frequency for the automated
weather broadcast. A description of the broadcast is
contained in subparagraph c. There is no two-way
communication capability. Most AWOS sites also
have a dial-up capability so that the minute-by-minute weather messages can be accessed via telephone.
5. AWOS information (system level, frequency,
phone number, etc.) concerning specific locations is
published, as the systems become operational, in the
A/FD, and where applicable, on published Instrument Approach Procedures. Selected individual
systems may be incorporated into nationwide data
collection and dissemination networks in the future.
c. AWOS Broadcasts. Computer-generated
voice is used in AWOS to automate the broadcast of
the minute-by-minute weather observations. In
addition, some systems are configured to permit the
addition of an operator-generated voice message;
e.g., weather remarks following the automated
parameters. The phraseology used generally follows
that used for other weather broadcasts. Following are
explanations and examples of the exceptions.
1. Location and Time. The location/name and
the phrase "AUTOMATED WEATHER OBSERVATION," followed by the time are announced.
(a) If the airport's specific location is
included in the airport's name, the airport's name is
announced.
EXAMPLE-
"Bremerton National Airport automated weather observation, one four five six zulu;"
"Ravenswood Jackson County Airport automated weather
observation, one four five six zulu."
(b) If the airport's specific location is not
included in the airport's name, the location is
announced followed by the airport's name.
EXAMPLE-
"Sault Ste. Marie, Chippewa County International Airport
automated weather observation;"
"Sandusky, Cowley Field automated weather
observation."
(c) The word "TEST" is added following
"OBSERVATION" when the system is not in
commissioned status.
EXAMPLE-
"Bremerton National Airport automated weather observation test, one four five six zulu."
(d) The phrase "TEMPORARILY INOPERATIVE" is added when the system is inoperative.
EXAMPLE-
"Bremerton National Airport automated weather observing system temporarily inoperative."
2. Visibility.
(a) The lowest reportable visibility value in
AWOS is "less than 1/4." It is announced as
"VISIBILITY LESS THAN ONE QUARTER."
(b) A sensor for determining visibility is not
included in some AWOS. In these systems, visibility
is not announced. "VISIBILITY MISSING" is
announced only if the system is configured with a
visibility sensor and visibility information is not
available.
3. Weather. In the future, some AWOSs are to
be configured to determine the occurrence of
precipitation. However, the type and intensity may
not always be determined. In these systems, the word
"PRECIPITATION" will be announced if precipitation is occurring, but the type and intensity are not
determined.
4. Ceiling and Sky Cover.
(a) Ceiling is announced as either "CEILING" or "INDEFINITE CEILING." With the
exception of indefinite ceilings, all automated ceiling
heights are measured.
EXAMPLE-
"Bremerton National Airport automated weather observation, one four five six zulu. Ceiling two thousand overcast;"
"Bremerton National Airport automated weather observation, one four five six zulu. Indefinite ceiling two hundred,
sky obscured."
(b) The word "Clear" is not used in AWOS
due to limitations in the height ranges of the sensors.
No clouds detected is announced as "NO CLOUDS
BELOW XXX" or, in newer systems as "CLEAR
BELOW XXX" (where XXX is the range limit of the
sensor).
EXAMPLE-
"No clouds below one two thousand."
"Clear below one two thousand."
(c) A sensor for determining ceiling and sky
cover is not included in some AWOS. In these
systems, ceiling and sky cover are not announced.
"SKY CONDITION MISSING" is announced only if
the system is configured with a ceilometer and the
ceiling and sky cover information is not available.
5. Remarks. If remarks are included in the
observation, the word "REMARKS" is announced
following the altimeter setting.
(a) Automated "Remarks."
(1) Density Altitude.
(2) Variable Visibility.
(3) Variable Wind Direction.
(b) Manual Input Remarks. Manual input
remarks are prefaced with the phrase "OBSERVER
WEATHER." As a general rule the manual remarks
are limited to:
(1) Type and intensity of precipitation.
(2) Thunderstorms and direction; and
(3) Obstructions to vision when the visibility is 3 miles or less.
EXAMPLE-
"Remarks ... density altitude, two thousand five hundred ...
visibility variable between one and two ... wind direction
variable between two four zero and three one zero
...observed weather ... thunderstorm moderate rain
showers and fog ... thunderstorm overhead."
(c) If an automated parameter is "missing"
and no manual input for that parameter is available,
the parameter is announced as "MISSING." For
example, a report with the dew point "missing" and
no manual input available, would be announced as
follows:
EXAMPLE-
"Ceiling one thousand overcast ... visibility three ...
precipitation ... temperature three zero, dew point missing
... wind calm ... altimeter three zero zero one."
(d) "REMARKS" are announced in the
following order of priority:
(1) Automated "REMARKS."
[a] Density Altitude.
[b] Variable Visibility.
[c] Variable Wind Direction.
(2) Manual Input "REMARKS."
[a] Sky Condition.
[b] Visibility.
[c] Weather and Obstructions to Vision.
[d] Temperature.
[e] Dew Point.
[f] Wind; and
[g] Altimeter Setting.
EXAMPLE-
"Remarks ... density altitude, two thousand five hundred ...
visibility variable between one and two ... wind direction
variable between two four zero and three one zero ...
observer ceiling estimated two thousand broken ...
observer temperature two, dew point minus five."
d. Automated Surface Observing System
(ASOS)/Automated Weather Sensor System
(AWSS). The ASOS/AWSS is the primary surface
weather observing system of the U.S. (See Key to
Decode an ASOS/AWSS (METAR) Observation,
FIG 7-1-8 and
FIG 7-1-9.) The program to install
and operate these systems throughout the U.S. is a
joint effort of the NWS, the FAA and the Department
of Defense. AWSS is a follow-on program that
provides identical data as ASOS. ASOS/AWSS is
designed to support aviation operations and weather
forecast activities. The ASOS/AWSS will provide
continuous minute-by-minute observations and
perform the basic observing functions necessary to
generate an aviation routine weather report (METAR) and other aviation weather information. The
information may be transmitted over a discrete VHF
radio frequency or the voice portion of a local
NAVAID. ASOS/AWSS transmissions on a discrete
VHF radio frequency are engineered to be receivable
to a maximum of 25 NM from the ASOS/AWSS site
and a maximum altitude of 10,000 feet AGL. At many
locations, ASOS/AWSS signals may be received on
the surface of the airport, but local conditions may
limit the maximum reception distance and/or altitude.
While the automated system and the human may
differ in their methods of data collection and
interpretation, both produce an observation quite
similar in form and content. For the "objective"
elements such as pressure, ambient temperature, dew
point temperature, wind, and precipitation accumulation, both the automated system and the observer use
a fixed location and time-averaging technique. The
quantitative differences between the observer and the
automated observation of these elements are
negligible. For the "subjective" elements, however,
observers use a fixed time, spatial averaging
technique to describe the visual elements (sky
condition, visibility and present weather), while the
automated systems use a fixed location, time
averaging technique. Although this is a fundamental
change, the manual and automated techniques yield
remarkably similar results within the limits of their
respective capabilities.
1. System Description.
(a) The ASOS/AWSS at each airport location
consists of four main components:
(1) Individual weather sensors.
(2) Data collection and processing units.
(3) Peripherals and displays.
(b) The ASOS/AWSS sensors perform the
basic function of data acquisition. They continuously
sample and measure the ambient environment, derive
raw sensor data and make them available to the
collection and processing units.
2. Every ASOS/AWSS will contain the
following basic set of sensors:
(a) Cloud height indicator (one or possibly
three).
(b) Visibility sensor (one or possibly three).
(c) Precipitation identification sensor.
(d) Freezing rain sensor (at select sites).
(e) Pressure sensors (two sensors at small
airports; three sensors at large airports).
(f) Ambient temperature/Dew point temperature sensor.
(g) Anemometer (wind direction and speed
sensor).
(h) Rainfall accumulation sensor.
3. The ASOS/AWSS data outlets include:
(a) Those necessary for on-site airport users.
(b) National communications networks.
(c) Computer-generated voice (available
through FAA radio broadcast to pilots, and dial-in
telephone line).
NOTE-
Wind direction broadcast over FAA radios is in reference
to magnetic north.
4. An ASOS/AWOS/AWSS report without
human intervention will contain only that weather
data capable of being reported automatically. The
modifier for this METAR report is "AUTO." When
an observer augments or backs-up an ASOS/AWOS/AWSS site, the "AUTO" modifier disappears.
5. There are two types of automated stations,
AO1 for automated weather reporting stations
without a precipitation discriminator, and AO2 for
automated stations with a precipitation discriminator.
As appropriate, "AO1" and "AO2" shall appear in
remarks. (A precipitation discriminator can determine the difference between liquid and
frozen/freezing precipitation).
NOTE-
To decode an ASOS/AWSS report, refer to
FIG 7-1-8 and
FIG 7-1-9.
REFERENCE-
A complete explanation of METAR terminology is located in AIM,
Paragraph
7-1-30, Key to Aerodrome Forecast (TAF) and Aviation
Routine Weather Report (METAR).
FIG 7-1-8
Key to Decode an ASOS/AWSS (METAR) Observation (Front)
FIG 7-1-9
Key to Decode an ASOS/AWSS (METAR) Observation (Back)
e.
TBL 7-1-1 contains a comparison of weather
observing programs and the elements reported.
f. Service Standards. During 1995, a government/industry team worked to comprehensively
reassess the requirements for surface observations at
the nation's airports. That work resulted in agreement
on a set of service standards, and the FAA and NWS
ASOS sites to which the standards would apply. The
term "Service Standards" refers to the level of detail
in weather observation. The service standards consist
of four different levels of service (A, B, C, and D) as
described below. Specific observational elements
included in each service level are listed in
TBL 7-1-2.
1. Service Level D defines the minimum
acceptable level of service. It is a completely
automated service in which the ASOS observation
will constitute the entire observation, i.e., no
additional weather information is added by a human
observer. This service is referred to as a stand alone D
site.
2. Service Level C is a service in which the
human observer, usually an air traffic controller,
augments or adds information to the automated
observation. Service Level C also includes backup of
ASOS elements in the event of an ASOS malfunction
or an unrepresentative ASOS report. In backup, the
human observer inserts the correct or missing value
for the automated ASOS elements. This service is
provided by air traffic controllers under the Limited
Aviation Weather Reporting Station (LAWRS)
process, FSS and NWS observers, and, at selected
sites, Non-Federal Observation Program observers.
Two categories of airports require detail beyond
Service Level C in order to enhance air traffic control
efficiency and increase system capacity. Services at
these airports are typically provided by contract
weather observers, NWS observers, and, at some
locations, FSS observers.
3. Service Level B is a service in which weather
observations consist of all elements provided under
Service Level C, plus augmentation of additional data
beyond the capability of the ASOS. This category of
airports includes smaller hubs or special airports in
other ways that have worse than average bad weather
operations for thunderstorms and/or freezing/frozen
precipitation, and/or that are remote airports.
4. Service Level A, the highest and most
demanding category, includes all the data reported in
Service Standard B, plus additional requirements as
specified. Service Level A covers major aviation
hubs and/or high volume traffic airports with average
or worse weather.
TBL 7-1-1
|
Weather Observing Programs
|
|
Element Reported
|
AWOS-A
|
AWOS-1
|
AWOS-2
|
AWOS-3
|
ASOS
|
Manual
|
|
Altimeter
|
X
|
X
|
X
|
X
|
X
|
X
|
|
Wind
|
|
X
|
X
|
X
|
X
|
X
|
|
Temperature/
Dew Point
|
|
X
|
X
|
X
|
X
|
X
|
|
Density Altitude
|
|
X
|
X
|
X
|
X
|
|
|
Visibility
|
|
|
X
|
X
|
X
|
X
|
|
Clouds/Ceiling
|
|
|
|
X
|
X
|
X
|
|
Precipitation
|
|
|
|
|
X
|
X
|
|
Remarks
|
|
|
|
|
X
|
X
|
TBL 7-1-2
|