METEOROLOGY FLIGHT PLANNING
Even though these AIRMET items are issued for widespread phenomena at least 3000 square miles
at any one time if the total area to be affected during the forecast period is very large, it could be that
only a small portion of this total area would be affected at any one time.
As with SIGMETs, the AIRMETs have unique headings that contain the bulletin type letter
following the area designator. For example, when an AIRMET for turbulence is issued, the
communications header might read "DFWT WA 210745," where "T" indicated it is an AIRMET
Tango bulletin. Also in the heading is the valid period expiration time, which is 6 hours after the
scheduled "valid beginning" time, or 6 hours and 15 minutes after the scheduled issuance time.
Each section begins with a text description of the type of AIRMET and a list of states and/or
geographical areas affected. As a minimum, each bulletin may indicate no significant weather of
that type is expected, and AIRMET Zulu always contains a freezing level line.
There are a few specific rules meteorologists follow when producing WAs that may be helpful for
understanding what weather is and is not forecast. Whenever a SIGMET is in effect, the
AIRMET bulletins for the same phenomena (in the same area) will contain a reference to the
appropriate SIGMET series. For example, "SEE SIGMET XRAY SERIES FOR SEV TURB
AREA." Additionally, when non-convective low-level wind shear (LLWSwind shear below
2000 feet AGL) is affecting or expected to affect an area of at least 3000 square miles, the
AIRMET Tango includes an LLWS potential statement as a separate line.
TRANSMISSION OF IN-FLIGHT WEATHER ADVISORIES
Since In-Flight Weather Advisories are designed primarily for en route information of changes in
the forecasts, an initial alert is normally transmitted over ATC frequencies. These alert
announcements give the type of advisory and frequency instruction, which indicates where further
information can be obtained, such as through the Hazardous In-Flight Weather Advisory Service
(HIWAS). Upon hearing an alert notice, if you are not familiar with the advisory or are in doubt,
you should tune in the appropriate frequency or contact the nearest FAA Flight Service Station
(FSS) or pilot-to-forecaster service (PMSV) to check whether the advisory is pertinent to your
flight. These advisories are broadcast during the valid periods, when they pertain to the area
within 150NM of the FSS. Times, frequencies, and further information can be found in the DOD
Flight Information Publication (En Route) Flight Information Handbook, Section C, and other
en route publications, as taught in the Instrument Flight Rules course.
Pilot Weather Reports (PIREPs) are a valuable source of information used to supplement ground
station weather observations. Air traffic facilities are required to solicit PIREPs whenever the
following conditions are reported or forecasted: ceilings at or below 5,000 feet, visibility at or
below 5 miles, thunderstorms and related phenomena, icing of a light degree or greater, turbulence
of moderate degree or greater, and wind shear. All pilots are urged to cooperate and promptly
volunteer reports on these conditions, and any other conditions pertinent to aviation, such as: cloud
bases, tops, and layers; flight visibility; precipitation; visibility restrictions; winds at altitude; and
temperatures aloft. Pilots are required to submit a PIREP under the following conditions:
SEVERE WEATHER WATCHES, MILITARY ADVISORIES, AND PIREPS