Plain English Meaning

The weather report is saying that less than once a minute, lightning is flashing — some of it inside the clouds, and some of it striking the ground.

Full Definition

A METAR remark indicating that lightning is occurring occasionally, with discharges observed both within clouds (in-cloud) and between clouds and the ground (cloud-to-ground). 'Occasional' in this context means lightning is observed at a rate of less than one flash per minute.

Context Anchor

Seen in the remarks section of a METAR when lightning is observed near the reporting station.

Derivation

A compressed code built from four standard METAR shorthand pieces: OCNL (occasional), LTG (lightning), IC (in-cloud), and CG (cloud-to-ground). Multiple lightning-type codes are run together without spaces, so LTGICCG means lightning of both IC and CG types.