What Does CB Mean in a METAR?
CB means cumulonimbus: thunderstorm cloud; severe turbulence, icing and wind-shear hazard. It stands for CumulonimBus.
CB in a real report
BKN020CB
What it changes for you
CB is the suffix that matters most in the cloud groups. It outranks the height
it is attached to.
A cumulonimbus brings severe or greater turbulence, severe icing, hail,
lightning and low level wind shear. BKN025CB is not a 2,500 foot ceiling with a
note on it. It is a thunderstorm, told through a cloud group.
Where it appears and where it does not
An automated station reports CB only when it can identify one, which usually
means lightning. No CB alongside a VCTS tells you the cell is close and
unclassified.
For this group, an augmented report from a human observer is the better source.
Related codes
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.
Frequently asked questions
What does CB mean in a METAR?
Cumulonimbus, the thunderstorm cloud. It is appended to a cloud group, as in BKN025CB. It brings severe turbulence, severe icing, hail, lightning and wind shear, and it is reported whenever it is present.
What is the difference between CB and TCU?
TCU is towering cumulus, a cell that is still building. CB is a mature thunderstorm cloud with an anvil and the full set of hazards. A TCU is the warning that a CB may be an hour away in the same air.