Plain English Meaning

BECMG means the weather is expected to change gradually sometime during the listed time window, and the new conditions will then stay that way. It tells the pilot what the weather is shifting to and roughly when.

Full Definition

A change indicator used in aviation forecasts (TAFs and area forecasts) showing that a gradual change in weather conditions is expected during a specified time period. The change is forecast to occur at an unspecified time within the BECMG window, and once the new conditions arrive they are expected to persist. The BECMG group is followed by a four-digit time pair indicating the beginning and ending hours (UTC) of the change period.

Context Anchor

Seen in aviation weather forecasts, including Area Forecasts, when forecast conditions are expected to change during a stated time window.

Derivation

From the English word 'becoming,' meaning 'in the process of changing into.' The shortened code BECMG keeps that same sense — the weather is in the process of becoming something else during the listed window.