Online Ground School (Private Pilot)
Lesson 13.4: Aviation Weather Forecasts
There are different types of forecasts that are used for the preflight. There are four types of forecasts that pilots need to be familiar with. Below we have combined SIGMETS and AIRMETS into the Area Forecast section.
Winds and Temperatures Aloft
TAF (Terminal Aerodrome Forecast)
TAF (Terminal Aerodrome Forecast) are weather reports for a five statute mile radius usually around a larger airport. TAFs are updated four times a day at 0000Z, 0600Z, 1200Z, and 1800Z and are issued for 24 or 30 hour periods.
TAFs are similar to METARs.
Example of a TAF:
More Complex TAF:
KLAX 311746Z 3118/0124 34004KT P6SM SCT040 BKN050 BKN140
FM311900 23010KT P6SM SCT030
FM010100 35006KT P6SM SKC
FM010600 02012KT P6SM SKC
FM011500 04010KT P6SM SKC
FM012200 VRB03KT P6SM SKC
KLGA 311732Z 3118/0124 17010KT P6SM BKN030 BKN200
FM312100 14010KT 3SM RA BR OVC015
FM010100 14012KT 1 1/2SM +RA OVC007 WS020/15040KT
FM010300 14012G20KT 1SM +RA OVC004 WS020/15040KT
FM010600 19012KT 4SM -RA BR OVC004 WS020/20045KT
FM010800 23012G22KT P6SM BKN015 WS020/24045KT
FM011200 27021G35KT P6SM BKN035
FM011800 30017G30KT P6SM SCT040
FM012200 31015KT P6SM SCT040
Area Forecast (FA)
Area Forecasts cover a large area of several states and covers general weather conditions, visual meteorological conditions (VMC). Area Forecast are issued three times a day and a valid for 18 hours.
AIRMET, SIGMET, Convective SIGMET are inflight weather advisories that have detailed information on potential hazardous weather to inflight aircraft. These advisories are in conjunction with the Area Forecast.
AIRMETs (WA) are issued every six hours, they include surface winds of 30 knots or greater, ceilings less than 1,000 feet and visibility less than 3 miles. AIRMETs are broken down into three categories:
Sierra – IFR and mountain obstructions.
Tango – Turbulence, low-level wind shear, strong surface winds.
Zulu – Icing, freezing levels.
Synopsis gives a detailed summary of the location, movement and types of weather pressure systems, fronts, and circulation patterns.
SIGMETs (WS) are unscheduled weather forecasts valid for four hours. If a SIGMET is for a hurricane or typhoon than the SIGMET is valid for six hours. These reports are for severe or extreme turbulence or CAT (clear air turbulence) not associated with thunderstorms, dust storms, and volcanic ash.
Convective SIGMETs are issued at 55 minutes past the hour and are valid for 2 hours. Convective SIGMETs cover the areas of the lower 48 states not including Alaska and Hawaii. They are broken up into three areas of the U.S.: E- eastern, C-central and W-western. They are numbered from 1-99 starting at time 00Z. These reports are for tornadoes, hail of 2 inches or greater in diameter, wind gusts up to 65 knots.
CONVECTIVE SIGMET 20C
VALID UNTIL 2055Z
(Convective SIGMET number 20 in the C-central region on the U.S.)
HNLC FA 311535
SYNOPSIS AND VFR CLD/WX
SYNOPSIS VALID UNTIL 011000
CLD/WX VALID UNTIL 010400...OUTLOOK VALID 010400-011000
SEE AIRMET SIERRA FOR IFR CLD AND MT OBSC.
TS IMPLY SEV OR GREATER TURB SEV ICE LOW LEVEL WS AND IFR COND.
NON MSL HGT INDICATED BY AGL OR CEILING.
A good way to help remember the three types of AIRMETs
Sierra (Seeing or Sight) IFR or cannot see train
Tango (T- for turbulence)
Zulu (Zero degrees) Icing or freezing
A HIGH PRESSURE RIDGE NORTH OF THE HAWAIIAN ISLANDS WILL
PRODUCE BREEZY TRADE WINDS THROUGH THE WEEK. MOSTLY VFR CONDITIONS WILL PREVAIL WITH PERIODS EARLY MORNING MVFR CEILINGS ALONG SOME WINDWARD SLOPES. ISOLATED TO SCATTERED SHOWERS WILL ARE POSSIBLE OVER THE NEXT FEW DAYS FAVORING WINDWARD AND MOUNTAIN AREAS.
Winds and Temperatures Aloft (FB)
Winds and Temperature Aloft (FB) forecast is for wind and temperature forecasts for specific areas of the U.S., Hawaii and Alaska. They are issued twice a day at 0000Z and 1200Z.
No wind or temperature is forecastted from the surface to but not including 3,000 feet.
For winds and Temperature from 3000 – FL240 (24,000 feet) it is read as is.
Example: ONT at 6000 the wind/temp is 0325-02
030⁰ at 25 knots -02⁰C
For winds greater than 99 knots but less than 199 knots or above 30,000 feet., it has to be converted with the equation: -50, +100 to the first four numbers. The last two numbers are always the temperature in negative Celsius.
Example: SAN at 30000 the wind/temp is 327747
50 – 32 = 18 becomes 180⁰ then 77 + 100 = 177 knots
So the wind is 180⁰ at 177 knots -47⁰C
If the forecast indicates ‘9900’ than the winds are calm or less than 5 knots or light and variable.