When 'BECMG' is used in a TAF, what does it signify?

'BECMG' in a Terminal Aerodrome Forecast (TAF) signifies a gradual permanent change in weather conditions. This term is used to indicate that the meteorological conditions are expected to evolve from one state to another over a specified time period. It implies that pilots should prepare for these changes, as they will be significant and lasting.

In TAFs, forecasters use 'BECMG' to clearly communicate that the coming weather changes are anticipated to develop steadily, rather than abruptly or temporarily. The gradual transition of weather elements, such as wind speed, visibility, or cloud cover, is crucial for flight planning and safety. Understanding this term is essential for pilots to make informed decisions based on long-term weather expectations rather than short-term variations.

Other terms in meteorological forecasting, while they may imply changes, differ in their meaning. For instance, rapid changes may be indicated by different terminology, emphasizing the need for pilots to discern the nature of changes based on the specific wording used in the forecasts.