What does the TAF forecast indicator TEMPO signify?

The TAF forecast indicator "TEMPO" is used to denote temporary weather conditions that are expected to occur within the forecast period but are projected to last for a limited duration, typically for less than one hour. This is important because it helps pilots and meteorologists identify short-lived weather phenomena that may impact flight operations, such as brief rain showers, gusty winds, or rapid changes in visibility.

In the context of the options provided, "any condition lasting less than one hour" accurately reflects the definition of "TEMPO," making it the correct choice. The emphasis on brevity in weather changes allows those interpreting the TAF to prepare for conditions that can quickly alter the flight environment but are not sustained long enough to affect the overall forecast significantly.

The other options do not align with the specific definition of "TEMPO." For instance, conditions lasting over an hour or those expected for less than half the time period misrepresent the temporary nature of these forecasts. Similarly, options that imply significantly broader or longer-lasting conditions do not conform to the precise usage of "TEMPO" in TAF reports. Understanding this distinction is vital for effective planning and safety in aviation.