Controllers must become familiar with pertinent weather information when coming on duty, and stay aware of current and forecasted weather information needed to perform ATC duties.
NOTE: Every phase of flight has the potential to be impacted by weather, and emphasis must be placed on gathering, reporting and disseminating weather information.
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. Null reports are critical to aviation weather forecasters and pilots and must be disseminated. Controllers must provide the information in sufficient detail to assist pilots in making decisions pertinent to flight safety.
NOTE: Routine PIREPs indicating a lack of forecasted weather conditions, for example, a lack of icing or turbulence, are also valuable to aviation weather forecasters and pilots. This is especially true when adverse conditions are expected or forecasted but do not develop or no longer exist.
FAA Order JO 7210.3, Para 10-3-1, SIGMET and PIREP Handling.
FAA Order JO 7110.10, Chapter 8, Section 2, Pilot Weather Report (UA/UUA).
Solicit PIREPs when requested, deemed necessary or any of the following conditions exists or is forecast for your area of jurisdiction:
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.
Visibility (surface or aloft) at or less than 5 miles.
Thunderstorms and related phenomena.
Turbulence of moderate degree or greater.
Icing of light degree or greater.
Braking action reports less than good.
Volcanic eruptions, ash clouds, and/or detection of sulfur gases in the cabin: sulfur dioxide (SO2) or hydrogen sulfide (H2S).
If only SO2 or H2S are detected with no reported volcanic ash clouds, ask the pilot if volcanic ash clouds are in the vicinity.
1. The smell of sulfur gases in the cockpit may indicate volcanic activity that has not yet been detected or reported and/or possible entry into an ash-bearing cloud. SO2 is identifiable as the sharp, acrid odor of a freshly struck match. H2S has the odor of rotten eggs.
2. Pilots may forward PIREPs regarding volcanic activity using the format described in the Volcanic Activity Reporting Form (VAR) as depicted in the AIM, Appendix 2.
FAA Order JO 7110.10, Para 8-2-5, Soliciting PIREPs
Record with the PIREPs:
When the PIREP involves icing include:
(a) Icing type and intensity.
(b) Air temperature in which icing is occurring.
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.
Relay pertinent PIREP information to concerned aircraft in a timely manner.
NOTE: Use the word gain and/or loss when describing to pilots the effects of wind shear on airspeed.
“Delta Seven Twenty-one, a Boeing Seven Thirty-seven, previously reported wind shear, loss of two five knots at four hundred feet.”
“Alaska One, a Boeing Seven Thirty-seven, previously reported wind shear, gain of two-five knots between niner hundred and six hundred feet, followed by a loss of five zero knots between five hundred feet and the surface.”
(e) Other concerned terminal or en route ATC facilities, including non-FAA facilities.
2-6-3. REPORTING WEATHER CONDITIONS
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:
Use the lower of the two observations (tower or surface) for aircraft operations.
Forward tower visibility observations to the weather observer.
Notify the weather observer when the tower observes the prevailing visibility decrease to less than 4 miles or increase to 4 miles or more.
Describe the wind as calm when the wind velocity is less than three knots.
Forward current weather changes to the appropriate control facility as follows:
When the official weather changes to a condition:
(a) Less than a 1,000-foot ceiling or below the highest circling minimum, whichever is greater.
(b) Where the visibility is less than 3 miles.
(c) Where conditions improve to values greater than those listed in (a) and (b).
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.
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.
If the receiving facility informs you that weather reports are not required for a specific time period, discontinue the reports.
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.
Controllers must issue pertinent information on observed/reported weather and chaff areas to potentially affected
aircraft. Define the area of coverage in terms of:
Azimuth (by referring to the 12-hour clock) and distance from the aircraft and/or
The general width of the area and the area of coverage in terms of fixes or distance and direction from fixes.
NOTE: Weather significant to the safety of aircraft includes conditions such as funnel cloud activity, lines of
thunderstorms, embedded thunderstorms, large hail, wind shear, microbursts, moderate to extreme turbulence
(including CAT), and light to severe icing.
WEATHER/CHAFF AREA BETWEEN (number) O'CLOCK AND (number) O'CLOCK (number) MILES,
(number) MILE BAND OF WEATHER/CHAFF FROM (fix or number of miles and direction from fix) TO (fix or number of
miles and direction from fix).
Inform any tower for which you provide approach control services of observed precipitation on radar which is
likely to affect their operations.
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.
NOTE: Weather and Radar Processor (WARP) does not display light intensity.
AREA OF (Intensity) PRECIPITATION BETWEEN (number) O'CLOCK AND (number) O'CLOCK, (number) MILES, MOVING
(direction) AT (number) KNOTS, TOPS (altitude). AREA IS (number) MILES IN DIAMETER.
1. “Area of heavy precipitation between ten o'clock and two o'clock, one five miles. Area is two five miles in
2. “Area of heavy to extreme precipitation between ten o'clock and two o'clock, one five miles. Area is two
five miles in diameter.”
TERMINAL. In STARS, correlate precipitation descriptors from subparagraph c as
Level 1 = LIGHT
Level 2 = MODERATE
Level 3 and 4 = HEAVY
Level 5 and 6 = EXTREME
When precipitation intensity information is not available.
AREA OF PRECIPITATION BETWEEN (number) O' CLOCK AND (number) O' CLOCK, (number) MILES. MOVING (direction) AT
(number) KNOTS, TOPS (altitude). AREA IS (number) MILES IN DIAMETER, INTENSITY UNKNOWN.
“Area of precipitation between one o'clock and three o'clock, three five miles moving south at one five knots,
tops flight level three three zero. Area is three zero miles in diameter, intensity unknown.”
NOTE: Phraseology using precipitation intensity descriptions is only applicable when the radar precipitation
intensity information is determined by NWS radar equipment or NAS ground based digitized radar equipment with
weather capabilities. This precipitation may not reach the surface.
EN ROUTE. When issuing Air Route Surveillance Radar (ARSR) precipitation
intensity use the following:
Describe the lowest displayable precipitation intensity as MODERATE.
Describe the highest displayable precipitation intensity as HEAVY to EXTREME.
AREA OF (Intensity) PRECIPITATION BETWEEN (number) O'CLOCK and (number) O'CLOCK, (number) MILES, MOVING
(direction) AT (number) KNOTS, TOPS (altitude). AREA IS (number) MILES IN DIAMETER.
1. “Area of moderate precipitation between ten o'clock and one o'clock, three zero miles moving east at two
zero knots, tops flight level three seven zero."
2. “Area of moderate precipitation between ten o'clock and three o'clock, two zero miles. Area is two five
miles in diameter.”
Controllers must ensure that the highest available level of precipitation intensity within their area of
jurisdiction is displayed unless operational/equipment limitations exist.
When requested by the pilot, provide radar navigational guidance and/or approve deviations around weather or chaff
areas. In areas of significant weather, plan ahead and be prepared to suggest, upon pilot request, the use of
An approval for lateral deviation authorizes the pilot to maneuver left or right within the lateral limits
specified in the clearance.
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
DEVIATION (restrictions, if necessary) APPROVED, MAINTAIN (altitude), (if necessary) MAINTAIN (speed), (if
applicable) EXPECT TO RESUME (SID/STAR, etc.) AT (NAVAID, fix/waypoint).
NOTE: After a climb via or descend via clearance has been issued, a vector/deviation off of a SID/STAR
cancels all published altitude and speed restrictions on the procedure. The aircraft's Flight Management
System (FMS) may be unable to process crossing altitude restrictions once the aircraft leaves the SID/STAR
lateral path. Without an assigned altitude, the aircraft's FMS may revert to leveling off at the altitude
set by the pilot, which may be the SID/STAR published top or bottom altitude.
If a pilot enters your area of jurisdiction already deviating for weather, advise the pilot of any additional
weather which may affect the route.
NOTE: When aircraft are deviating around weather and transitioning from sector to sector, unless previously
coordinated, the receiving controller should not assume that the transferring controller has issued weather
affecting the aircraft's route of flight.
If traffic and airspace (i.e., special use airspace boundaries, LOA constraints) permit, combine the approval
for weather deviation with a clearance on course.
DEVIATION (restrictions if necessary) APPROVED, WHEN ABLE, PROCEED DIRECT (name of NAVAID/WAYPOINT/FIX)
DEVIATION (restrictions if necessary) APPROVED, WHEN ABLE, FLY HEADING (degrees), VECTOR TO JOIN (airway)
1. “Deviation 20 degrees right approved, when able proceed direct O'Neill VORTAC and advise.” En Route:
The corresponding fourth line entry is “D20R/ONL” or “D20R/F.”
2. “Deviation 30 degrees left approved, when able fly heading zero niner zero, vector to join J324 and
advise.” En Route: In this case the free text character limitation prevents use of fourth line
coordination and verbal coordination is required.
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.
DEVIATION (restrictions if necessary) APPROVED, ADVISE CLEAR OF WEATHER.
“Deviation North of course approved, advise clear of weather.”
En Route: In this case the corresponding fourth line entry is “DN,” and the receiving controller must
provide a clearance to rejoin the route in accordance with paragraph 2-1-15 c.
When a deviation cannot be approved as requested because of traffic, take an alternate course of action that
provides positive control for traffic resolution and satisfies the pilot's need to avoid weather.
UNABLE REQUESTED DEVIATION, FLY HEADING (heading), ADVISE CLEAR OF WEATHER.
UNABLE REQUESTED DEVIATION, TURN (number of degrees) DEGREES (left or right) VECTOR FOR TRAFFIC, ADVISE CLEAR
“Unable requested deviation, turn thirty degrees right vector for traffic, advise clear of weather.”
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.
“(call sign) assigned heading three three zero for weather avoidance”
The inclusion of a NAVAID, waypoint, or /F in the fourth line data indicates that the pilot has been
authorized to deviate for weather and must rejoin the route at the next NAVAID or waypoint in the route of
“Deviation twenty degrees right approved, when able proceed direct O'Neill VORTAC and advise.” In this
case, the corresponding fourth line entry is “D20R/ONL” or “D20R/F.”
The absence of a NAVAID, waypoint, or /F in the fourth line indicates that:
(a) 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.
“Deviation twenty degrees right approved, advise clear of weather.”
(b) The free text character limitation prevents the use of fourth line coordination. Verbal coordination
“Deviation 30 degrees left approved, when able fly heading zero niner zero, vector to join J324 and
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.
NOTE: Anomalous propagation (AP) is a natural occurrence affecting radar and does not in itself constitute a
weather circuit failure.
2-6-5. DISSEMINATING OFFICIAL WEATHER INFORMATION
TERMINAL. Observed elements of weather information must be disseminated as follows:
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.
Specific values, such as ceiling and visibility, may be transmitted if obtained by one of the following means:
You are properly certificated and acting as official weather observer for the elements being reported.
NOTE: USAF controllers do not serve as official weather observers.
You have obtained the information from the official observer for the elements being reported.
The weather report was composed or verified by the weather station.
The information is obtained from a FAA approved automation surface weather system.
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), 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.
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.
ATTENTION ALL AIRCRAFT. HAZARDOUS WEATHER INFORMATION (SIGMET, Convective SIGMET, AIRMET, Urgent Pilot Weather
Report (UUA), or Center Weather Advisory (CWA), Number or Numbers) FOR (specific weather phenomenon) WITHIN
(geographical area) AVAILABLE ON FLIGHT SERVICE FREQUENCIES.
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.