The lightning activity level guide for observers describes clouds, storm and lightning frequency criteria for classifying lightning events. Because the objective is to describe the lightning activity, lightning counts take precedence over the cloud-storm-rain narrative description. For instance, if the clouds should fit the LAL 3 descriptive criteria, but the lightning averages three cloud-to-ground discharges per minute, the LAL should be classified as a 4.
Also included in the lightning activity level guide for observers is the relative frequency of occurrence of the various LAL. For instance, LAL 6 is a rare event not likely to occur on more than 1 or 2 percent of the lightning days.
The observation of lightning (the LAL) should include what has happened within a 25 to 30-mile radius of the station.
The fire weather observer must obtain as much information as possible from all available sources to insure an accurate LAL observation. The fire weather forecaster has other sources of information on thunderstorm activity, and therefore, should be consulted if there is confusion over the selection of an LAL.
Lightning Activity Level Guide for Weather Observers
| Individual Storm Cell Cloud to Ground Lightning Discharge (cg) | |||||
|---|---|---|---|---|---|
| LAL | Cloud & Storm Development | Counts cg/5 min |
Counts cg/15 min |
Avg. cg/min |
% of T-storm Days |
| 1 | No T-storms | - | - | - | -- |
| 2 | Cumulus clouds are common but only a few reach the towering cumulus stage. A single thunderstorm must be confirmed in the observation area. The clouds produce mainly virga, but light rain will occasionally reach the ground. Lightning is very infrequent. | 1-5 | 1-8 | <1 | 10 |
| 3 | Towering cumulus covers less than two-tenths of the sky. Thunderstorms are few, but two to three must occur within the observation area. Light to moderate rain will reach the ground, and lighting is infrequent. | 6-10 | 9-15 | 1-2 | 35 |
| 4 | Towering cumulus covers two to three-tenths of the sky. Thunderstorms are scattered and more than three must occur within the observation area. Moderate rain is common and lightning is frequent. | 11-15 | 16-25 | 2-3 | 35 |
| 5 | Towering cumulus and thunderstorms are numerous. They cover more than three-tenths and occasionally obscure the sky. Rain is moderate to heavy and lightning is frequent and intense. | >15 | >25 | >3 | 18 |
| 6 | Similar to LAL 3 except thunderstorms are dry. | <2 | |||
April 2008