Reports concerning thunderstorms shall be made whenever a thunderstorm begins or ends. In the body of the observation, TS may be coded by itself or with precipitation types such as RA, SN, PL, GS or GR. The intensity attached to it shall be the intensity ascribed to the precipitation as described in paragraph 15-14b(4). In the remarks section, the report shall include the following:

a.  Type and frequency of lightning

b.  Time of beginning, ending, or both, to the nearest minute

c.  Location, in accordance with the rules given in paragraph 11-7, Rules for Phenomena Not Occurring at the Point of Observation, or 15-32, Thunderstorm Location

d.  Direction toward which the storm is moving (omit if unknown)

Figure 11-9, Type and Frequency of Lightning, presents the types and frequencies of lightning to be reported. The above remarks shall be updated and included with the time of beginning, ending, or both on the next transmitted METAR observation if not previously reported in a METAR observation. The format for the remarks is given in paragraph 15-30, Beginning and Ending of Precipitation, 15-31, Beginning and Ending of Thunderstorms, 15-32, Thunderstorm Location, and 15-33, Hailstone Size.

A thunderstorm is considered to begin at the station when thunder is heard, overhead lightning is observed and the local noise level is such as might prevent hearing thunder, or lightning is detected by an automated sensor within ten miles of the airport. A thunderstorm is considered to have ended 15 minutes after the last occurrence of any of the above criteria. When the time of beginning or ending of a thunderstorm is reported in the remarks section of a SPECI observation, it need not be reported again until the next transmitted METAR observation if not previously reported in a METAR observation. If previously reported in a METAR observation, the time need not be reported again.

Hail shall be reported in an observation whenever it begins or ends, and in all observations taken while it is occurring. Times of beginnings and endings shall be included in the remarks section (NA LAWRS). All observations concerning hail shall report the diameter of the largest hailstones in the remarks section in 1/4 inch increments (NA LAWRS). No intensity shall be assigned to hail. The format for reporting hail is given in paragraph 15-33, Hailstone Size.

If SPECI is because of hail, then begin/end time shall be recorded in the remarks. When the time of beginning or ending of hail is reported in the remarks section of a SPECI observation, it need not be recorded again until the next transmitted METAR observation if not previously reported in a METAR observation. If previously reported in a METAR observation, the time need not be reported again.

When lightning is observed, the type, frequency, and location shall be reported in the remarks section of METAR and SPECI observations. The format for reporting lightning is given in paragraph 15-29, Lightning Frequency. Figure 11-9 presents definitions for the type and frequency of lightning.

Lightning (LTG). Lightning is defined as any of the various forms of visible electrical discharge produced by thunderstorms. Four main types of lightning can be distinguished:

a.  Cloud to ground lightning (CG) is lightning occurring between a cloud and the ground.

b.  In-cloud discharges (IC) are a type of lightning that takes place within a thunder cloud.

c.  Cloud to cloud discharges (CC) are streaks of lightning reaching from one cloud to another.

d.  Air Discharges (CA) are streaks of lightning which pass from a cloud to the air, but do not strike the ground.

Figure 11-9. Type and Frequency of Lightning

A squall is reported in the body of a METAR or SPECI only when there is a sudden increase in wind speed of at least 16 knots, the speed rises to 22 knots or more, and lasts for at least one minute.