In aviation meteorology, a trend type forecast (TTF), also known simply as a trend, is a weather forecast written by a person on location at a major airport or military base. A TTF is a professionally considered forecast for weather over a two-hour period,[1] and is based on an actual weather report, such as a METAR or SPECI and appended to the end of it.[1] A TTF is similar to or sometimes in addition to a TAF, a terminal aerodrome forecast, but during the TTF's validity period is considered superior to a TAF.[citation needed]