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Fox News Weather Center

Dry Lightning to Increase Wildfire Risk Across Western US, Canada

The combination of excessive heat and dry thunderstorms in many areas will add to the wildfire threat in the western part of United States and Canada through much of July.

High temperatures over much of the interior western U.S. will range from 95 to 105 F this week. Some places in the Southwest will get even hotter.

The nature of the current weather pattern tends to favor thunderstorm formation, but low doses of moisture in many cases will stop drenching rainfall from reaching widespread areas of the West.

The risk of lightning-induced thunderstorms will diminish in the Northwest by midweek as a punch of dry air moves in from the Pacific Ocean. However, the risk of thunderstorms will continue in British Columbia and Alberta, and in many parts of the southwestern U.S.

According to AccuWeather Western Weather Expert Ken Clark, "With the onset of the monsoon season, the chance of fires has greatly risen in the West."

The western U.S. monsoon is associated with the northward spread of tropical moisture, mainly from Mexico. This moisture then becomes trapped beneath a lingering high pressure system. Daytime heating, combined with the moisture produces thunderstorms. How moist the air is near the ground determines whether or not significant rain is able to reach the ground before evaporating.

According to the U.S. National Interagency Fire Center, there was an average of 10,600 wildland fires started by lightning during the period from 2001 to 2013.

Activities such as fishing, camping or hiking as thunderstorms rapidly develop during the midday and afternoon hours could be dangerous. Storms over the high country in the West tend to spring up faster than storms in the East where the elevation is generally lower.

The number of deaths from people struck by lightning while fishing and camping in the U.S. dwarfs that of golfing a NOAA report stated.

"Lightning can strike miles away from a thunderstorm with and without rain," Clark said.

Because of the ongoing heat and low humidity, in addition to being a potential target for lightning when in wide open places, people need to be extremely careful with campfires, outdoor power equipment and parking vehicles over high brush.

"Lightning, along with man, accidental or deliberate are the two main causes of wildfires in the West," Clark said.

According to the National Interagency Fire Center, humans cause an average of 62,100 fires in the U.S. each year.

In western Canada, it has been a rough wildfire season already, AccuWeather Senior Meteorologist Brett Anderson said.

"The smoke from fires in British Columbia and Alberta is being blown downstream into parts of the Upper Midwest and occasionally farther to the southeast," Anderson said.

The smoke has been contributing to rounds of poor air quality in the Midwest and to some extent dimming sunshine, producing hazy conditions and making for colorful sunsets as far downstream as parts of the Atlantic Seaboard.

Parts of western Canada will experience a couple of rounds of thunderstorms this week. A few of the storms will bring significant moisture at the local level, but many may not.

The same is true for the southwestern U.S., which will have near daily storms. As humidity levels rise in the Southwest, the chances of getting a drenching storm versus a dry storm will increase this month.

By the time the moisture reaches the Northwest, a higher percentage of the storms will bring little or no rainfall.