In meteorological forecasts, certain codes are used to indicate expected changes in weather conditions. These codes help pilots and aviation professionals anticipate how weather may evolve over a given period.

Three common codes used in TAF (Terminal Aerodrome Forecast) reports are BECMG, TEMPO, and NOSIG.

BECMG (Becoming)

It indicates that a lasting change in weather conditions is expected to occur during the forecast period. It suggests that one set of prevailing conditions will gradually transition to another set over time. BECMG is typically used when fluctuations in weather are expected to last for more than an hour, making it appropriate for longer-lasting changes.

This code is helpful when meteorologists expect a steady transition in conditions, such as a gradual clearing of clouds or the onset of rain over an extended period.

TEMPO (Temporary)

It indicates temporary fluctuations in the forecast weather conditions. Unlike BECMG, which predicts long-lasting changes, TEMPO suggests that the change will be brief—lasting less than an hour in each instance.

TEMPO is used when there are short-lived weather disturbances, like brief periods of heavy rain or gusty winds.

NOSIG (No Significant Change)

NOSIG stands for No Significant Change and indicates that the prevailing weather conditions are expected to remain stable over the next two hours. NOSIG gives assurance to pilots that no major weather changes are expected during the forecast window, allowing for consistent planning and operations.