Thunderstorms in Alaska

As we move into summer weather, clouds change from widespread layered (or stratus) to a discrete cauliflower type of cumulus cloud. These cumulus clouds, due primarily to ground heating by the sun, otter develop into thunderstorms. Many Alaskan forest fires are caused by lightning from these thunderstorms. Because these fires often remain undetected for a long time, they account for most of the forest acreage burned (about 1 million acres per year.) A single thunderstorm lasts almost 20 minutes. Thunderstorms are associated with updrafts inside and downdrafts below it. These drafts can be as fast as 50 knots. The sudden wind shifts associated with downdrafts under a storm are most dangerous to aircraft.

Thunderstorms do not occur uniformly over the State. Very few, if any, are recorded north of the Brooks Range. Of the few preferred areas, the most extensive thunderstorm formation occurs in the mountainous region between the Yukon and Tanana rivers, extending into Lake Minchumina. Fairbanks is in the middle of this active region. Lightning from thunderstorms could occur between two clouds or from cloud to ground. The thunder associated with the former is heard as a rumbling noise while the latter is heard as a crack. Cloud to ground lightning is what causes damage to trees and can kill animals.

If caught in a treeless plain during a thunderstorm, lay flat until the storm passes, as lightning prefers to strike elevated objects which act as antennas. One person or animal in a group can act as an antenna causing all to be struck by lightning. (Herds of caribou sometimes found dead on the plains are so killed.) Another simple precaution is to avoid standing under trees or touching their trunks. Tall trees around your house, especially if you are living in the hills, will help deflect lightning; also make sure your television antenna is well grounded.