When would a "TEMPO" forecast be included in a TAF?

A "TEMPO" forecast is included in a TAF to indicate that temporary fluctuations or short-term variations in weather conditions are expected within a specified period of the overall forecast. This segment is utilized when the forecast anticipates that certain weather phenomena, such as showers, thunderstorms, or other significant weather changes, will occur for limited durations—typically not lasting longer than one hour at a time and not more than half of the total forecast period.

This type of forecast is essential for aviators, as it provides critical information on transient weather conditions that may necessitate adjustments to flight operations, such as approach and landing techniques. Since the "TEMPO" forecast covers only brief episodes of variation, it is distinct from more stable conditions that either remain constant throughout the forecast period or signify permanent changes.

In contrast, a permanent alteration in weather would not necessitate a "TEMPO" designation, as it would simply be reflected in the overall TAF without highlighting periods of fluctuation. Likewise, a forecast representing stable conditions or absence of any anticipated weather changes would not apply to the "TEMPO" scenario, as it is specifically intended for those brief, expected anomalies.