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Weather Advisories
Weather Advisories consist of Airman's Meteorological Information
(AIRMETs), Significant Meteorological Information (SIGMETs), Convective SIGMETs,
Center Weather Advisories (CWAs), and Severe Weather Forecast Alerts (AWW),
commonly called Alert Weather watches. These products warn of hazardous or
potentially hazardous conditions (IFR conditions, turbulence, icing, thunderstorms, etc.).
Typically, to be included in weather advisory, the phenomena must be
widespread (i.e., covering an area 3,000 square miles or more).
Pilots should therefore always be alert to local or localized areas of
hazardous weather which may not warrant the issuance of a weather
advisory. Remember - the absence of an advisory does not necessarily mean the
absence of hazardous weather.
The AIRMET contains hazardous weather conditions, generally
of concern to small aircraft. SIGMETs pertain to potentially
hazardous that may affect the safety of all aircraft. Convective
SIGMETs and Weather Watches are issued for thunderstorm or
thunderstorm-related phenomena. Center Weather Advisories are
advisories of adverse weather conditions, possibly hazardous to some
aircraft, which are applicable to the airspace under the control of the
issuing center. They may precede the issuance or amendment of
SIGMETs and AIRMETs, or provide warnings for phenomena too small to be
included in other advisories.
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. Other weather advisories are
unscheduled and issued as needed.
Aviation Routine Weather Report (METAR)
The international METAR and SPECI (special) weather codes
replaced the North American Surface Aviation Weather Report (SA)
and SP formats in 1996. These reports are specific aviation weather
observations taken at designated reporting sites throughout the United
States. They communicate the actual weather conditions at the
reporting location. Normally, the observation sites are located on
airports, but occasionally nearby outside the airport boundaries. In
some rare cases, a METAR may be reported at a remote location
(mountain passes).
METAR observations are usually taken and transmitted hourly at
about 50 minutes past each hour. These observations are generally
available within a few minutes after the hour. Special observations (SPECI)
are taken whenever changing weather conditions warrant.
Example of a METAR report:
METAR KRDU 0101502 10009KT 10SM SHRA - OVC050 23/15
A2982 RMK RAB40 FQT LTG DSNT SW SLP094
Translation: Aviation Routine Weather Report, Raleigh-Durham
Airport, observation the first day of the month at 0150 ZULU, wind
from 100 degrees true at 9 knots; visibility 10 statute miles; light rain showers;
ceiling 5,000 feet overcast, temperature 23 degrees C; dew point 15 C altimeter
29.82 inches. Remarks: Rain began at 40 minutes past the hour;
frequent lightning to the distant southwest; sea level pressure 1009.4
Hectopascals/ millibarH.
(Note: When providing wind information to departing or arriving
aircraft, terminal facilities will provide winds relative to magnetic
north).
Pilot Weather Reports (PIREPs)
The need for objective PIREPs cannot be overstated. Pilot
reports are presently the best source of inflight turbulence and icing
information, and often the only source of weather conditions enroute. Although
PIREPs can be filed with any ATC facility, to the extent possible,
pilots should file these reports with Flight Watch or a Flight Service
Station to ensure dissemination throughout the system.
The following information should be included in a PIREP:
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Your location (ideally, in reference to a VOR or airport, or a significant
geographical landmark),altitude, and type of aircraft.
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Sky cover, including amount (i.e., FEW, SCT, BKN, OVC);
bases and tops reports.
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Flight visibility and weather encountered.
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Outside air temperature (OAT).
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Other significant weather data (e.g., distant weather observed).
Example of a PIREP:
KLYH UA /OV KRIC-KLYH180010/TM 1415/FL065/TP
C152/SK SCT-BKN030 TOPS040/ OVC100/WX FV05M
HZ/TA 06/TB LGT/RM MOD TURBC SFC-045 DURGC
KRIC
Translation: Pilot report; from Richmond, VA, to 10 nautical miles
south of Lynchburg, VA; time - 14152; altitude 6,500 feet MSL; type
aircraft, Cessna 152; cloud bases 3,000 feet MSL, coverage scattered to
broken, tops 4,000 feet MSL, higher cloud bases 10,000 feet MSL
coverage overcast, flight visibility 5 statute miles, haze, temperature
6C; light turbulence at 6500 ft.; remarks - moderate turbulence from
the surface to 4,500 feet MSL during climbout from Richmond.
Area Forecasts (FA)
Area Forecasts are 12-hour aviation forecasts plus a 6-hour
categorical outlook giving general descriptions of VFR sky and
weather conditions that affect aircraft operations. The Area Forecast is
not a stand-alone product and must be used in conjunction with the
AIRMET Bulletins; specifically, AIRMET SIERRA (IFR and
mountain obscurations), TANGO (turbulence), and ZULU (icing and
freezing levels), which are issued on a scheduled basis.
Heights of cloud bases are referenced to height above mean sea
level (MSL), unless otherwise noted as above ground level (AGL) or
ceilings (CIG). Cloud tops are always given in MSL.
Categorical outlook terms, describing general ceiling and visibility
conditions for outlook planning purposes, are defined as follows :
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 |  |  |  | Ceilings less than 500 feet and/or visibility less than 1
statute mile | Ceilings less than 1,000 feet and/or visibility less than 3
statute miles | Ceilings between 1,000 to 3,000 feet
and/or visibility 3 to 5 statute miles, inclusive | Ceilings greater than 3,000 feet and visibility greater
than 5 statute miles |  |  |  |  |
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The causes of IFR or MVFR are indicated by either ceiling or
restrictions to visibility, or both. The contraction CIG (for ceiling)
and/or weather and obstruction to visibility symbols are used. If winds
of 30 knots or greater are forecast for the outlook period, the word
WIND is also included for all categories, including VFR.
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Example: LIFR CIG - Low IFR due to a low ceiling.
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Example: IFR FG - IFR due to visibility restricted by fog.
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Example: MVFR CIG HZ FU -- Marginal VFR due both to
ceiling and to visibility restricted by haze and smoke.
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Example: IFR CIG RA WIND - IFR due both to low ceiling
and to visibility restricted by rain; the surface wind is expected to be
30 knots or greater.
Area Forecasts, each covering a broad geographical area are issued
3 times a day in the contiguous United States, and 4 times a day
in Alaska and Hawaii.
Issuance times differ from geographic area to area. Specific
schedule times for your location can be obtained by calling the nearest
FSS. These forecasts are amended as required.
Aerodrome Forecasts (TAF)
Aerodrome Forecasts are issued for specific airports and are valid
for a 5 statute mile radius from the center of the runway complex.
They contain information on the expected surface winds, visibility;
weather, obstructions to vision, and cloud coverage and heights. They
are valid for a 24 hour period.
Aerodrome Forecasts are issued 4 times a day. Each forecast is
amended according to prescribed criteria, as required.
Aerodrome forecasts are presented in the following order:
An example of a TAF:
KBOS 0411452 1212 34015G25KT 5SM SHSN-
SCT010 BKN018 TEMPO 1215 1/2SM SHSN VV008
BECMG 15-17 33012G22KT P6SM BKN050
Translation: Boston Aerodrome Forecast for the 4th day of the
month, valid time 122-122. Surface wind from 340 degrees at 15 knots with
peak gusts to 25 knots; visibility 5 statute miles; light snow showers;
scattered clouds at 1,000 feet AGL; ceiling 1,800 feet broken AGL;
occasionally, visibility one half mile in moderate snow showers;
indefinite ceiling 800 feet (an indefinite ceiling represents a surface based
phenomena obscuring the whole sky). Becoming between 15Z and 172 surface wind from
330 degrees at 12 knots with gusts to 22 knots; visibility greater than 6 miles;
ceiling 5,000 feet broken AGL.
Wind and Temperatures Aloft Forecasts (FD)
Winds and temperatures aloft forecasts provide wind direction,
speed, and temperature for selected locations. Winds between forecast
points can be calculated by interpolation. Winds and temperatures
aloft forecasts are 6-hour, 12-hour, and 24-hour forecasts to the
nearest 10 degrees, relative to true north, wind speed in knots, and
temperature in degrees Celsius for selected altitudes. No forecasts are
provided for reporting levels within about 1,500 feet (or less) of the
surface. Temperature is omitted for the first 3,000 foot level (or at any
level within 2,500 feet of the surface).
Forecasts are generated twice daily from 00002 and 12002
radiosonde upper air observations. These forecasts are available about
4 hours after each observation.
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 |  |  |  | 3,000 | 2925 |  |  |  |  |
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 |  |  |  | 6,000 | 283300 |  |  |  |  |
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 |  |  |  | 9,000 | 293004 |  |  |  |  |
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Partial translation: Kennedy Airport, at 6,000 feet MSL, the
forecast winds are from 280 degrees true at 33 knots with a temperature of
0 degrees C.
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