Thunderstorm Activity
A thunderstorm is considered to have begun and to be "occurring at the ship" when thunder is first heard. It may also be considered as occurring when hail is falling or when lightning is observed in the immediate vicinity of the ship when the local noise is such that the thunder cannot be heard. A thunderstorm is reported as ended 15 minutes after the last occurrence of these criteria.
The following information should be reported for thunderstorms:
- The time of beginning, ending, or both, to the nearest minute.
- The location of each storm center with respect to the ship, including distance in nm if known.
- The direction toward which the storm is moving.
- Frequency, type, and location of lightning.
Type and Frequency of Lightning
| Type | Contraction | Frequency | Contraction |
|---|---|---|---|
| Cloud to Ground | CG | Occasional (< 1 flash/min) | OCNL |
| In-Cloud | IC | Frequent (1-6 flashes/min) | FRQ |
| Cloud-Cloud | CC | Continuous (>6 flashes/min) | CNS |
| Cloud-Air | CA |
Look at these two images and decide which type of lightning is occurring.
The correct answers are a) Cloud-to-Cloud and b) Cloud-to-Ground.
Thunderstorm clouds, specifically cumulonimbus or towering cumulus, should be reported with the contractions CB and TCU, respectively, as these are significant cloud types indicating potential weather hazards. Report CB or TCU in the Remarks section along with their relative direction from the ship, distance from the ship, and direction in which they are moving. The criteria for reporting are detailed in the U.S. Navy Manual for Ship's Surface Weather Observations, Table II.1.1.