Thunderstorm (TS)

TS reports a thunderstorm. It is a descriptor, so it combines with the precipitation it is accompanied by: TSRA is a thunderstorm with rain, TSGR a thunderstorm with hail, TSSN with snow.

TS on its own is meaningful and not an omission. It means thunder has been heard or lightning seen at the station, but no precipitation is reaching it — the cell is overhead or close, and its rain is falling elsewhere. VCTS reports a thunderstorm in the vicinity, meaning between roughly 8 and 16 km from the aerodrome: not over the field, but close enough to affect the approach and to move.

A thunderstorm group is the most consequential thing a short report can contain. It implies severe turbulence, wind shear, downdraughts and possible hail regardless of what the wind and visibility groups say, which is why a cumulonimbus at any height disqualifies CAVOK. Intensity qualifiers apply to the precipitation, not to the storm — +TSRA is a thunderstorm with heavy rain, not a heavy thunderstorm.