Chart 1: Lightning Activity Level

 

 
 

LAL Cloud and Storm Development

Individual Storm Cell Cloud to Ground Lightning Discharge

cg/5 min cg/15 min (cg/min) coverage 

1 No thunderstorms        
2 Cumulus clouds are common but only a few reach the towering cumulus stage. A single thunderstorm must be confirmed in the rating area. The clouds mostly produce virga, but light rain will occasionally reach the ground. Lightning is very infrequent.
1-5
1-8
1
1-14%
3 Cumulus clouds are common. Swelling and towering cumulus cover less than 2/10 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 lightning is infrequent.
6-10
9-15
1-2
<25%
4 Swelling cumulus and towering cumulus cover 2 3/10 of the sky. Thunderstorms are scattered, but more than three must occur within the observation area. Moderate rain is commonly produced, and lightning is frequent.
11-15
16-25
2-3
25-54%
5
  1. Towering cumulus and thunderstorms are numerous. They cover more than 3/10 and occasionally obscure the sky. Rain is moderate to heavy, and lightning is frequent and intense. 
15
25
3
>54%
6
  • Same as #3 but dry (little or no rain 
  • reaches the ground).
  •