Statistically, way more fires are started by humans than by lightning. However, more of the large fires began with a lightning strike.
Large fires burning across the Pacific Northwest and the Northern Rockies are producing widespread smoke that is now stretching almost across the country. Most of these fires were started by lightning, in a pattern this summer caused by a strong monsoon.
“But Curtis!” you may say, “Isn't the monsoon a heavy rain?” Well no, not necessarily. The definition of monsoon is a seasonal prevailing wind shift in parts of the world that can at times bring heavy rain to certain areas.
In the summer months across the west, a seasonal monsoon high develops. This high pressure produces heavy rain and thunderstorms over the four corners states, which makes up the majority of this region's annual precipitation.
At times this moisture can reach Montana and the Pacific Northwest, but more frequently these storms dry out and have less moisture to work with by the time they reach this far north, but still produce lightning. Some of Montana's worst fire seasons are with a strong monsoon high in the summer producing more storms that create more numerous lightning strikes with little moisture.
The strong monsoon high this year has also left Central Plains states like Nebraska and Kansas with drought, steering moisture away from this region into New Mexico and Arizona.
As summer is winding down, so has the monsoon high which has all but disappeared.