Section 6. Weather Information
Become familiar with pertinent weather information when coming on duty, and stay aware of current weather information needed to perform ATC duties.
2-6-2. HAZARDOUS INFLIGHT WEATHER ADVISORY SERVICE (HIWAS)
Controllers must advise pilots of hazardous weather that may impact operations within 150 NM of their sector or area of jurisdiction. Hazardous weather information contained in HIWAS broadcasts includes Airmen's Meteorological Information (AIRMET), Significant Meteorological Information (SIGMET), Convective SIGMET (WST), Urgent Pilot Weather Reports (UUA), and Center Weather Advisories (CWA). Facilities must review alert messages to determine the geographical area and operational impact for hazardous weather information broadcasts. The broadcast is not required if aircraft on your frequency(s) will not be affected.
a. Controllers within commissioned HIWAS areas must broadcast a HIWAS alert on all frequencies, except emergency frequency, upon receipt of hazardous weather information. Controllers are required to disseminate data based on the operational impact on the sector or area of control jurisdiction.
b. Controllers outside of commissioned HIWAS areas must:
1. Advise pilots of the availability of hazardous weather advisories. Pilots requesting additional information should be directed to contact the nearest Flight Watch or Flight Service.
2. Apply the same procedure when HIWAS outlets, or outlets with radio coverage extending into your sector or airspace under your jurisdiction, are out of service.
c. Terminal facilities have the option to limit hazardous weather information broadcasts as follows: Tower cab and approach control facilities may opt to broadcast hazardous weather information alerts only when any part of the area described is within 50 NM of the airspace under their jurisdiction.
2-6-3. PIREP INFORMATION
Significant PIREP information includes reports of strong frontal activity, squall lines, thunderstorms, light to severe icing, wind shear and turbulence (including clear air turbulence) of moderate or greater intensity, volcanic eruptions and volcanic ash clouds, detection of sulfur gases (SO2 or H2S) in the cabin, and other conditions pertinent to flight safety.
a. Solicit PIREPs when requested or when one of the following conditions exists or is forecast for your area of jurisdiction:
1. Ceilings at or below 5,000 feet. These PIREPs must include cloud base/top reports when feasible.
TERMINAL. Ensure that at least one descent/climb-out PIREP, including cloud base/s, top/s, and other related phenomena, is obtained each hour.
EN ROUTE. When providing approach control services, the requirements stated in TERMINAL above apply.
2. Visibility (surface or aloft) at or less than 5 miles.
3. Thunderstorms and related phenomena.
4. Turbulence of moderate degree or greater.
5. Icing of light degree or greater.
6. Wind shear.
7. Volcanic ash clouds.
8. Detection of sulfur gases (SO2 or H2S), associated with volcanic activity, in the cabin.
9. TERMINAL. Braking Action Advisories are in effect.
b. Record with the PIREPs:
2. Aircraft position.
3. Type aircraft.
5. When the PIREP involves icing include:
(a) Icing type and intensity.
(b) Air temperature in which icing is occurring.
c. Obtain PIREPs directly from the pilot, or if the PIREP has been requested by another facility, you may instruct the pilot to deliver it directly to that facility.
d. Handle PIREPs as follows:
1. Relay pertinent PIREP information to concerned aircraft in a timely manner.
2. EN ROUTE. Relay all operationally significant PIREPs to the facility weather coordinator.
3. TERMINAL. Relay all operationally significant PIREPs to:
(a) The appropriate intrafacility positions.
(b) The FSS serving the area in which the report was obtained.
(c) Other concerned terminal or en route ATC facilities, including non-FAA facilities.
(d) Use the word gain and/or loss when describing to pilots the effects of wind shear on airspeed.
2-6-4. WEATHER AND CHAFF SERVICES
a. Issue pertinent information on observed/reported weather and chaff areas. When requested by the pilot, provide radar navigational guidance and/or approve deviations around weather or chaff areas.
1. Issue weather and chaff information by defining the area of coverage in terms of azimuth (by referring to the 12-hour clock) and distance from the aircraft or by indicating the general width of the area and the area of coverage in terms of fixes or distance and direction from fixes.
2. When a deviation cannot be approved as requested and the situation permits, suggest an alternative course of action.
b. In areas of significant weather, plan ahead and be prepared to suggest, upon pilot request, the use of alternative routes/altitudes.
c. Inform any tower for which you provide approach control services of observed precipitation on radar which is likely to affect their operations.
d. Use the term “precipitation” when describing radar-derived weather. Issue the precipitation intensity from the lowest descriptor (LIGHT) to the highest descriptor (EXTREME) when that information is available. Do not use the word “turbulence” in describing radar-derived weather.
2. “Area of heavy precipitation between ten o'clock and two o'clock, one five miles. Area is two five miles in diameter.”
3. “Area of heavy to extreme precipitation between ten o'clock and two o'clock, one five miles. Area is two five miles in diameter.”
e. When precipitation intensity information is not available.
f. EN ROUTE. When issuing Air Route Surveillance Radar (ARSR) precipitation intensity use the following:
1. Describe the lowest displayable precipitation intensity as MODERATE.
2. Describe the highest displayable precipitation intensity as HEAVY to EXTREME.
2. “Area of moderate precipitation between ten o'clock and three o'clock, two zero miles. Area is two five miles in diameter.”
g. When operational/equipment limitations exist, controllers must ensure that the highest available level of precipitation intensity within their area of jurisdiction is displayed.
h. The supervisory traffic management coordinator-in-charge/operations supervisor/controller-in-charge must verify the digitized radar weather information by the best means available (e.g., pilot reports, local tower personnel, etc.) if the weather data displayed by digitized radar is reported as questionable or erroneous. Errors in weather radar presentation must be reported to the technical operations technician and the air traffic supervisor must determine if the digitized radar derived weather data is to be displayed and a NOTAM distributed.
2-6-5. CALM WIND CONDITIONS
TERMINAL. Describe the wind as calm when the wind velocity is less than three knots.
2-6-6. REPORTING WEATHER CONDITIONS
a. When the prevailing visibility at the usual point of observation, or at the tower level, is less than 4 miles, tower personnel must take prevailing visibility observations and apply the observations as follows:
1. Use the lower of the two observations (tower or surface) for aircraft operations.
2. Forward tower visibility observations to the weather observer.
3. Notify the weather observer when the tower observes the prevailing visibility decrease to less than 4 miles or increase to 4 miles or more.
b. Forward current weather changes to the appropriate control facility as follows:
1. When the official weather changes to a condition which is below 1,000-foot ceiling or below the highest circling minimum, whichever is greater, or less than 3 miles visibility, and when it improves to a condition which is better than those above.
2. Changes which are classified as special weather observations during the time that weather conditions are below 1,000-foot ceiling or the highest circling minimum, whichever is greater, or less than 3 miles visibility.
c. Towers at airports where military turbo-jet en route descents are routinely conducted must also report the conditions to the ARTCC even if it is not the controlling facility.
d. If the receiving facility informs you that weather reports are not required for a specific time period, discontinue the reports. The time period specified should not exceed the duration of the receiving controller's tour of duty.
e. EN ROUTE. When you determine that weather reports for an airport will not be required for a specific time period, inform the FSS or tower of this determination. The time period specified should not exceed the duration of receiving controller's tour of duty.
2-6-7. DISSEMINATING WEATHER INFORMATION
TERMINAL. Observed elements of weather information must be disseminated as follows:
a. General weather information, such as “large breaks in the overcast,” “visibility lowering to the south,” or similar statements which do not include specific values, and any elements derived directly from instruments, pilots, or radar may be transmitted to pilots or other ATC facilities without consulting the weather reporting station.
b. Specific values, such as ceiling and visibility, may be transmitted if obtained by one of the following means:
1. You are properly certificated and acting as official weather observer for the elements being reported.
2. You have obtained the information from the official observer for the elements being reported.
3. The weather report was composed or verified by the weather station.
4. The information is obtained from an official Automated Weather Observation System (AWOS) or an Automated Surface Observation System (ASOS).
c. Differences between weather elements observed from the tower and those reported by the weather station must be reported to the official observer for the element concerned.