Forecast Times

METEOROLOGY FLIGHT PLANNING

CHAPTER ONE

Forecast Times

The six-digit number following the message heading indicates the forecast period of the entire

TAF, which is usually 24 hours (Figure 1-21). The first two digits represent the date of the

forecast. The second two digits indicate the beginning hour of the forecast, and the final two

digits indicate the ending hour of the forecast. For example, 260909 means that the forecast

begins at 0900Z on the 26th day of the month and covers the 24-hour period up to but not

including 0900Z the next day. U.S. civil stations include date and time of transmission prior to

the forecast period (i.e., 091720Z 091818).

KNSE TAF 260909 28004KT 9000 HZ SCT020 SCT200 QNH2998INS

Figure 1-21 TAF Time Group

Whenever the forecast is an AMD, COR, or RTD, the times may not be for a 24-hour period and

will be indicated accordingly. When USN/USMC stations amend, correct, or have a routine

delayed forecast, a remark will be appended to the last line of the forecast with the appropriate

time (e.g., AMD2218).

Winds

Wind direction is forecasted to the nearest 10 degrees true, in the direction from which the wind

will be blowing (Figure 1-22). If wind direction is expected to vary by 60 degrees or more, the

limits of variability will be noted as a remark, e.g., WND 270V350. The contraction VRB can

only be used to replace direction when forecasted wind speed is 6 knots or less, or in more rare

cases when it is impossible to forecast a single wind direction, such as for thunderstorms.

KNSE TAF 260909 28004KT 9000 HZ SCT020 SCT200 QNH2998INS

Figure 1-22 TAF Winds

Forecasted wind speeds and gust data are given in whole knots; if the wind speed is over 100

knots, then three digits are used. Calm winds are represented by "00000" for the wind group.

"G" will be included to indicate gusts when the peak wind exceeds the average wind by 10 knots

or more. Presently all U.S. winds are in knots and the contraction KT will end these wind

groups. Some overseas stations use KPH (kilometers per hour) or MPS (meters per second).

Visibility, Weather, and Obstructions to Vision

For TAFs, forecasted prevailing visibility is reported in meters and rounded down to the nearest

reportable value (Figure 1-23). U.S. civil stations, however, will report visibility in statute miles

(Figure 1-24). Whenever the prevailing visibility is forecasted to be 9000 meters or less (6 miles

or less) the weather or obstructions to vision causing the reduced visibility will be included using

AVIATION ROUTINE WEATHER REPORTS AND TERMINAL AERODROME

FORECASTS 1-19