What Does BECMG Mean in a TAF?

BECMG means a gradual change over the period given; after it, the new conditions prevail. It stands for BECoMinG.

BECMG in a real report

BECMG 0606/0608 21015KT

What it changes for you

BECMG 2906/2908 24010KT says the wind becomes 240 at 10 sometime between 0600Z and 0800Z, and stays there.

The trap is what it leaves out. That group named a wind and nothing else, so the visibility and cloud from before it are still in force. A period with no cloud group in it is not a period with no cloud.

Reading the window

The change is expected to happen at some point inside the window rather than at a stated moment. Before the window, the old conditions. After it, the new ones. During it, either.

For a tight arrival time that lands inside a BECMG window, plan for the worse of the two states, because the forecast has explicitly declined to tell you which one you will get.

Related codes

• TEMPO
• FM051800
• PROB30
• AMD

Decode a report containing this code

Paste a METAR, TAF, PIREP or SIGMET into the WxDecoder decoder. Every group comes back in plain English. The raw code sits beside it, so you can check the decode rather than trust it.