Qualifiers of Intensity or Proximity
- Light
Moderate (no qualifier)
+ Heavy or well-developed
VC in the Vicinity

Qualifier Descriptor
MI Shallow
BC Patches
DR Low Drifting
BL Blowing
SH Showers
TS Thunderstorm
FZ Freezing
PR Partial

Precipitation
DZ Drizzle
RA Rain
SN Snow
SG Snow Grains
IC Ice Crystals
PE Ice Pellets
GR Hail
GS Small Hail or Snow Pellets (less than 1/4 inch in diameter)
UP Unknown precipitation (automated stations only)

Obscuration
BR Mist (Foggy conditions with visibilities greater than 5/8 statute mile)
FG Fog (visibility 5/8 statute mile or less)
FU Smoke
DU Dust
SA Sand
HZ Haze
PY Spray
VA Volcanic Ash

Other
PO Well-Developed Dust/Sand Whirls
SQ Squalls
FC Funnel Cloud
+FC Well-Developed Funnel Cloud, Tornado or Waterspout
SS Sandstorm
DS Duststorm

Obscurations to vision will be forecast whenever the prevailing visibility is forecast to be 6 statute miles or less.

If no significant weather is expected to occur during a specific time period in the forecast, the weather group is omitted for that time period. If, after a time period in which significant weather has been forecast, a change to a forecast of no significant weather occurs, the contraction NSW (No Significant Weather) will appear as the weather group in the new time period. However, NSW is only included in the BECMG or TEMPO groups.

Sky Condition
TAF sky condition forecasts use the METAR format. Cumulonimbus clouds (CB) are the only cloud type forecast in TAFs.

When the sky is obscured due to a surface-based phenomenon, vertical visibility (VV) into the obscuration is forecast. The format for vertical visibility is VV followed by a three-digit height in hundreds of feet.

Note: Ceiling layers are not designated in the TAF code. For aviation purposes, the ceiling is the lowest broken or overcast layer or vertical visibility into a complete obscuration.

Examples:
SKC - Sky clear
SCT005 BKN025CB BKN250 - Five hundred scattered, ceiling two thousand five hundred broken cumulonimbus clouds, two five thousand broken.
VV008 - Indefinite ceiling eight hundred

Optional Data (Wind Shear)
Wind shear is the forecast of non-convective low level winds (up to 2000 feet) and is entered after the sky conditions when wind shear is expected. The forecast includes the height of the wind shear followed by the wind direction and wind speed at the indicated height. Height is given in hundreds of feet AGL up to and including 2,000 feet. Wind shear is encoded with the contraction WS followed by a three-digit height, slant character, and winds at the height indicated in the same format as surface winds. The wind shear element is omitted if not expected to occur.

Example:
WS010/18040KT - Low level wind shear at one thousand, wind one eight zero at four zero.

Probability Forecast
The probability or chance of thunderstorms or other precipitation events occurring, along with associated weather conditions (wind, visibility, and sky conditions).

The PROB40 group is used when the occurrence of thunderstorms or precipitation is in the 30% to less than 50% range, thus the probability value 40 is appended to the PROB contraction. This is followed by a four-digit group giving the beginning hour and ending hour of the time period during which the thunderstorms or precipitation is expected.

Note: PROB40 will not be shown during the first six hours of a forecast.
Examples:
PROB40 2102 1/2SM +TSRA - Chance between 2100Z and 0200Z of visibility one-half thunderstorm, heavy rain.
PROB40 1014 1SM RASN - Chance between 1000Z and 1400Z of visibility one rain and snow.
PROB40 2024 2SM FZRA - Chance between 2000Z and 0000Z of visibility two freezing rain.

Forecast Change Indicators
The following change indicators are used when either a rapid, gradual, or temporary change is expected in some or all of the forecast meteorological conditions. Each change indicator marks a time group within the TAF report.

FROM Group
The FM group is used when a rapid change, usually occurring in less than one hour, in prevailing conditions is expected. Typically, a rapid change of prevailing conditions to more or less a completely new set of prevailing conditions is associated with a synoptic feature passing through the terminal area (cold or warm frontal passage). Appended to the FM indicator is the four-digit hour and minute the change is expected to begin and continues until the next change group or until the end of the current forecast.

A FM group will mark the beginning of a new line in a TAF report. Each FM group contains all the required elements -- wind, visibility, weather, and sky condition. Weather will be omitted in FM groups when it is not significant to aviation. FM groups will not include the contraction NSW.

Examples:
FM0100 SKC - After 0100Z sky clear
FM1430 OVC020 - After 1430Z ceiling two thousand overcast

BECOMING Group
The BECMG group is used when a gradual change in conditions is expected over a longer time period, usually two hours. The time period when the change is expected is a four-digit group with the beginning hour and ending hour of the change period which follows the BECMG indicator. The gradual change will occur at an unspecified time within this time period. Only the conditions are carried over from the previous time group.

Example:
OVC012 BECMG 1416 BKN020 - Ceiling one thousand two hundred overcast. Then a gradual change to ceiling two thousand broken between 1400Z and 1600Z.

TEMPORARY Group
The TEMPO group is used for any conditions in wind, visibility, weather, or sky condition which are expected to last for generally less than an hour at a time (occasional), and are expected to occur during less than half the time period. The TEMPO indicator is followed by a four-digit group giving the beginning hour and ending hour of the time period during which the temporary conditions are expected. Only the changing forecast meteorological conditions are included in TEMPO groups. The omitted conditions are carried over from the previous time group.

Examples:
SCT030 TEMPO 1923 BKN030 - Three thousand scattered with occasional ceilings three thousand broken between 1900Z and 2300Z.
4SM HZ TEMPO 0006 2SM BR HZ - Visibility four in haze with occasional visibility two in mist and haze between 0000Z and 0600Z.

TAF Coverage:
--IFR conditions
--Mountain obscurations
--Moderate turbulence, icing, 30 kt winds
--Coincides with AIRMET information
--Three times a day. A 12 hour forecast with 6 hour outlook that is `printed 15 minutes before an hour to all stations
--Hazards/flight precautions
--IFR conditions/thunderstorms
--Icing, turbulence, obscurations
--Visibility when below 5 miles
--Winds over 30 kts.
--Synopsis is a Total overview that is good for six hours
--Clouds and Weather good for 12 hours referenced to mean sea level
--Ceilings referenced to ground level
--Outlook good for 18 hours
--TAF excludes temperature, turbulence and icing forecasts.
--Ceiling is not designated: defined as lowest broken or overcast layer or the vertical visibility.

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