Appears in METARs and TAFs
TEMPO
Temporary fluctuations that come and go without changing the underlying forecast.
TEMPOTEMPO introduces conditions expected to occur temporarily during the stated period. It does not replace the prevailing forecast — it describes departures from it.
Two limits define it. Each individual occurrence is expected to last less than one hour, and all occurrences together are expected to cover less than half the stated period. If a condition were expected to last longer than that, the forecaster would use BECMG, or state it as the prevailing condition, instead.
This makes TEMPO a planning tool rather than a description of the likely state of the aerodrome. TEMPO 2000 RA in a period whose baseline is 9999 means the aerodrome is expected to be clear for most of it, with spells of rain reducing visibility to 2 000 m — brief, repeated, and each one short. It can be combined with a probability group: PROB30 TEMPO means a 30 % chance that those temporary fluctuations occur at all.
In a real report
TAF LIRF 311100Z 3112/0118 20008KT 9999 FEW025 TEMPO 3114/3120 3000 TSRA BKN012CB
The baseline stays 10 km and few cloud. Between 14:00 and 20:00, expect intermittent thunderstorms with rain cutting visibility to 3 000 m — each spell under an hour, together less than half the six-hour window.