Aviation Weather Services

Aviation Forecasts 7. Forecast significant weather—weather phenomena Observed weather condition reports are often used in the are coded in the TAF reports in the same format as creation of forecasts for the same area. A variety of different the METAR. forecast products are produced and designed to be used in the 8. Forecast sky condition—given in the same format as preflight planning stage. The printed forecasts that pilots need the METAR. Only cumulonimbus (CB) clouds are to be familiar with are the terminal aerodrome forecast (TAF), forecast in this portion of the TAF report as opposed aviation area forecast (FA), inflight weather advisories to CBs and towering cumulus in the METAR. (SIGMET, AIRMET), and the winds and temperatures aloft 9. Forecast change group—for any significant weather forecast (FB). change forecast to occur during the TAF time period, the expected conditions and time period are included Terminal Aerodrome Forecasts (TAF) in this group. This information may be shown as from A TAF is a report established for the five statute mile (FM), and temporary (TEMPO). “FM” is used when a radius around an airport. TAF reports are usually given for rapid and significant change, usually within an hour, is larger airports. Each TAF is valid for a 24 or 30-hour time expected. “TEMPO” is used for temporary fluctuations period and is updated four times a day at 0000Z, 0600Z, of weather, expected to last less than 1 hour. 1200Z, and 1800Z. The TAF utilizes the same descriptors and abbreviations as used in the METAR report. The TAF 10. PROB30—a given percentage that describes the includes the following information in sequential order: probability of thunderstorms and precipitation occurring in the coming hours. This forecast is not 1. Type of report—a TAF can be either a routine forecast used for the first 6 hours of the 24-hour forecast. (TAF) or an amended forecast (TAF AMD). 2. ICAO station identifier—the station identifier is the Example: same as that used in a METAR. TAF KPIR 111130Z 1112/1212 3. Date and time of origin—time and date (081125Z) TEMPO 1112/1114 5SM BR of TAF origination is given in the six-number code FM1500 16015G25KT P6SM SCT040 BKN250 with the first two being the date, the last four being FM120000 14012KT P6SM BKN080 OVC150 PROB30 the time. Time is always given in UTC as denoted by 1200/1204 3SM TSRA BKN030CB the Z following the time block. FM120400 1408KT P6SM SCT040 OVC080 4. Valid period dates and times—The TAF valid period TEMPO 1204/1208 3SM TSRA OVC030CB (0812/0912) follows the date/time of forecast origin group. Scheduled 24 and 30 hour TAFs are issued Explanation: four times per day, at 0000, 0600, 1200, and 1800Z. Routine TAF for Pierre, South Dakota…on the 11th day of The first two digits (08) are the day of the month for the month, at 1130Z…valid for 24 hours from 1200Z on the the start of the TAF. The next two digits (12) are the 11th to 1200Z on the 12th…wind from 150° at 12 knots… starting hour (UTC). 09 is the day of the month for visibility greater than 6 SM…broken clouds at 9,000 feet… the end of the TAF, and the last two digits (12) are temporarily, between 1200Z and 1400Z, visibility 5 SM in the ending hour (UTC) of the valid period. A forecast mist…from 1500Z winds from 160° at 15 knots, gusting period that begins at midnight UTC is annotated as 00. to 25 knots visibility greater than 6 SM…clouds scattered If the end time of a valid period is at midnight UTC, at 4,000 feet and broken at 25,000 feet…from 0000Z wind it is annotated as 24. For example, a 00Z TAF issued from 140° at 12 knots…visibility greater than 6 SM…clouds on the 9th of the month and valid for 24 hours would broken at 8,000 feet, overcast at 15,000 feet…between 0000Z have a valid period of 0900/0924. and 0400Z, there is 30 percent probability of visibility 3 5. Forecast wind—the wind direction and speed forecast SM…thunderstorm with moderate rain showers…clouds are coded in a five-digit number group. An example broken at 3,000 feet with cumulonimbus clouds…from would be 15011KT. The first three digits indicate the 0400Z…winds from 140° at 8 knots…visibility greater than direction of the wind in reference to true north. The 6 miles…clouds at 4,000 scattered and overcast at 8,000… last two digits state the windspeed in knots appended temporarily between 0400Z and 0800Z…visibility 3 miles… with “KT.” Like the METAR, winds greater than 99 thunderstorms with moderate rain showers…clouds overcast knots are given in three digits. at 3,000 feet with cumulonimbus clouds…end of report (=). 6. Forecast visibility—given in statute miles and may be in whole numbers or fractions. If the forecast is greater than six miles, it is coded as “P6SM.” 13-9