Terminal area forecasts (TAFs) are aviation weather forecasts. They are very precise and typically cover the next 24 to 36 hours from the time they’re issued. Each period within the TAF provides information on the winds, clouds and precipitation expected to occur. There are also optional sections that may appear for temporarily occurring weather (less than an hour) and for weather than may occur (30% and 40% probability). The latter is usually only for “bad” weather that could impact flight safety.
Gordon’s Rule for TAFs is simple: The longer the forecast, the more unsettled (aka “crappy” (a highly technical term)) the weather is going to be.
Here’s the TAF for Ottawa that was issued over the lunch hour:
TAF CYOW 011738Z 0118/0218 26005KT P6SM BKN120 OVC220 FM012000 05005KT P6SM -SN OVC070 TEMPO 0120/0122 4SM -SN FM012200 06010KT 2SM -SN VV015 TEMPO 0122/0124 4SM -SN OVC050 FM020000 06012KT 11/2SM -SN VV012 TEMPO 0200/0202 3/4SM -SN VV008 FM020200 06015G25KT 1/2SM SN BLSN VV005 FM020500 06020G30KT 1/4SM +SN BLSN VV002 BECMG 0208/0210 04015G25KT FM021100 35015G25KT 3/4SM -SN BLSN VV008 FM021300 31018G28KT 2SM -SN BLSN OVC025 FM021700 29018G28KT 5SM BLSN BKN030 RMK NXT FCST BY 012100Z