Section 6. Weather Information

2-6-1. FAMILIARIZATION

Controllers mustbecome familiar with pertinent weather information when coming on duty, and stay aware of current and forecasted weather information needed to perform ATC duties.

2-6-2. PIREP SOLICITATION AND DISSEMINATION

Emphasis must be placed on the solicitation and dissemination of Urgent (UUA) and Routine (UA) PIREPs. Timely dissemination of PIREPs alerts pilots to weather conditions and provides information useful to forecasters in the development of aviation forecasts. PIREPs also provide information required by ATC in the provision of safe and efficient use of airspace. This 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, braking action, volcanic eruptions and volcanic ash clouds, detection of sulfur gases in the cabin, and other conditions pertinent to flight safety. Controllers must provide the information in sufficient detail to assist pilots in making decisions pertinent to flight safety.

  1. Solicit PIREPs when requested, deemed necessary or any 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 bases, tops and cloud coverage when available. Additionally, when providing approach control services, ensure that at least one descent/climb–out PIREP and other related phenomena is obtained each hour.
    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. Braking action reports less than good.
    8. Volcanic ash clouds.
    9. Detection of sulfur gases (SO2 or H2S), associated with volcanic activity, in the cabin.
  2. Categorize PIREPs as follows:
    1. URGENT. The following weather phenomena must be classified as an URGENT PIREP (UUA):
      1. Tornadoes, funnel clouds, or waterspouts.
      2. Severe or extreme turbulence (including clear air turbulence).
      3. Severe icing.
      4. Hail.
      5. Low‐level wind shear (LLWS). For the safety of light aircraft, classify low‐level wind shear PIREPs as UUA if the pilot reports airspeed fluctuations of 10 knots or more. Classify reports of low‐level wind shear with airspeed fluctuations less than 10 knots as routine. If airspeed fluctuation is not reported, classify PIREP as UUA.
      6. Volcanic eruption, ash clouds, and/or detection of sulfur gases (H2S or SO2) in the cabin, however, if a pilot only reported the smell of H2S or SO2 in the cabin and confirmed no volcanic ash clouds were present, classify the report as a ROUTINE PIREP.
      7. Any other weather phenomena reported which in your opinion may be hazardous, or potentially hazardous, to flight operations.
    2. ROUTINE. Classify as ROUTINE (UA) all PIREPs received except those listed above.
  3. Record with the PIREPs:
    1. Time.
    2. Aircraft position.
    3. Type aircraft.
    4. Altitude or range of altitudes.
    5. When the PIREP involves turbulence, include:
      1. Duration (occasional, intermittent, or continuous).
      2. Intensity (light, moderate, severe, or extreme).
    6. When the PIREP involves icing, include:
      1. Icing type and intensity (trace, light, moderate, or severe).
      2. Air temperature in which icing is occurring.
  4. 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.
  5. Disseminate 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:
      1. The appropriate intrafacility positions.
      2. The OS/CIC for long line dissemination via an FAA approved electronic system (for example, AIS-R, or similar systems); or,
      3. Outside Alaska: The overlying ARTCC's Flight Data Unit for long-line dissemination.
      4. Alaska Only: The FSS serving the area in which the report was obtained.
      5. Other concerned terminal or en route ATC facilities, including non-FAA facilities.

2-6-3. REPORTING WEATHER CONDITIONS

  1. 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 visibilityobservations 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.
  2. Describe the wind as calm when the wind velocity is less than three knots.
  3. Forward current weather changes to the appropriate control facility as follows:
    1. When the official weather changes to a condition:
      1. Less than a 1,000-foot ceiling or below the highest circling minimum, whichever is greater.
      2. Where the visibility is less than 3 miles.
      3. Where conditions improve to values greater than those listed in (a) and (b).
    2. When 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.
  4. 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.
  5. If the receiving facility informs you that weather reports are not required for a specific time period, discontinue the reports.
  6. 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.

2-6-4. ISSUING WEATHER AND CHAFF AREAS

  1. Controllers must issue pertinent information on observed/reported weather and chaff areas to potentially affected aircraft. Define the area of coverage in terms of:
    1. Azimuth (by referring to the 12‐hour clock) and distance from the aircraft and/or
    2. The general width of the area and the area of coverage in terms of fixes or distance and direction from fixes.
  2. Inform any tower for which you provide approach control services of observed precipitation on radar which is likely to affect their operations.
  3. Use the term “weather” when describing satellite‐derived weather, e.g., Offshore Precipitation Capability (OPC), using the phraseology in subparagraph a above. Do not issue intensity based on satellite‐derived weather.
  4. 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.
    1. LIGHT.
    2. MODERATE.
    3. HEAVY.
    4. EXTREME.
  5. TERMINAL: In STARS, correlate precipitation descriptors from subparagraph c as follows:
    1. Level 1 = LIGHT
    2. Level 2 = MODERATE
    3. Levels 3 and 4 = HEAVY
    4. Levels 5 and 6 = EXTREME
  6. When precipitation intensity information is not available.
  7. EN ROUTE. When issuing 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.
  8. Controllers must ensure that the highest available level of precipitation intensity within their area of jurisdiction is displayed unless operational/equipment limitations exist.
  9. When requested by the pilot, provide radar navigational guidance and/or approve deviations around weather or chaff areas. In areas of significantweather, plan ahead and be prepared to suggest, upon pilot request, the use of alternative routes/altitudes.
    1. An approval for lateral deviation authorizes the pilot to maneuver left or right within the lateral limits specified in the clearance.
    2. When approving a weather deviation for an aircraft that had previously been issued a crossing altitude, including climb via or descend via clearances, issue an altitude to maintain and, if necessary, assign a speed along with the clearance to deviate. If you intend on clearing the aircraft to resume the procedure, advise the pilot.
    3. If a pilot enters your area of jurisdiction already deviating for weather, advise the pilot of any additional weather which may affect the route.
    4. If traffic and airspace (i.e., special use airspace boundaries, LOA constraints) permit, combine the approval for weather deviation with a clearance on course.
    5. If traffic or airspace prevents you from clearing the aircraft on course at the time of the approval for a weather deviation, instruct the pilot to advise when clear of weather.
  10. When a deviation cannot be approved as requested because of traffic, take an alternate course of action that provides positive control for trafficresolution and satisfies the pilot's need to avoid weather.
  11. When forwarding weather deviation information, the transferring controller must clearly coordinate the nature of the route guidance service being provided. This coordination should include, but is not limited to: assigned headings, suggested headings, pilot-initiated deviations. Coordination can be accomplished by: verbal, automated, or predetermined procedures. Emphasis should be made between: controller assigned headings, suggested headings, or pilot initiated deviations.
  12. En Route Fourth Line Data Transfer
    1. The inclusion of /(NAVAID) or /(waypoint), when preceded by the designated characters for weather deviations, indicates that a pilot has been authorized to deviate for weather and rejoin the route at the specified NAVAID or waypoint. The use of /F, following the designated weather deviation characters, indicates that a pilot has been authorized to deviate and rejoin the route of flight at the next NAVAID or waypoint in the flight plan.
    2. The absence of a NAVAID, waypoint, or /F in the fourth line indicates that:
      1. The pilot has been authorized to deviate for weather only, and the receiving controller must provide a clearance to rejoin the route in accordance with paragraph 2-1-15c.
      2. The free text character limitation prevents the use of fourth line coordination. Verbal coordination is required.
  13. 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. DISSEMINATING OFFICIAL WEATHER INFORMATION

TERMINAL.Observed elements of weather information must be disseminated as follows:

  1. 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.
  2. 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 a FAA approved automation surface weather system.
  3. 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.

2-6-6. HAZARDOUS INFLIGHT WEATHER ADVISORY

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 the advisories includes Airmen's Meteorological Information (AIRMET) (except over the CONUS), 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 of hazardous weather information. Advisories are not required if aircraft on your frequency(s) will not be affected.

  1. Controllers must broadcast a hazardous inflight weather advisory 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. Pilots requesting additional information must be directed to contact the nearest Flight Service.
  2. 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.
  3. EN ROUTE.ERAM. Controllers must electronically acknowledge hazardous weather information messages after appropriate action has been taken.