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Spokane, Washington  Est. May 19, 1883
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Weathercatch: Those recent lightning strikes? Blame the desert monsoons

The Rillito River rolls along west of Swan Road after a powerful storm with heavy rain hit Tucson, Ariz., on July 23. Weather conditions in the drought-stricken Southwest helped spawn storms here in the Pacific Northwest.  (Rick Wiley/Arizona Daily Star)
The Rillito River rolls along west of Swan Road after a powerful storm with heavy rain hit Tucson, Ariz., on July 23. Weather conditions in the drought-stricken Southwest helped spawn storms here in the Pacific Northwest. (Rick Wiley/Arizona Daily Star)
By Nic Loyd and Linda Weiford For The Spokesman-Review

During the early morning hours one day last week, the Inland Northwest experienced a rare sound and sight.

Rainfall.

No measurable rain had fallen since June 15. Finally, on July 21, a band of brief thunderstorms lumbered through the region between 3 and 7:30 a.m.

Although we didn’t get much rain – only 0.12 of an inch in Spokane and less than a 10th of an inch in many other places – those storms still packed a punch. Why? Because they produced multiple lightning strikes.

The series of early morning storms with origins in the Southwest desert set off 250 lightning strikes across the Inland Northwest, with 29 reported in Spokane County, according to the National Weather Service Spokane.

With exceptionally dry, hot conditions in our region, cloud-to-ground lightning bolts ignited several wildfires in parts of Eastern Washington and North Idaho. The Sherwood Fire on the Spokane Reservation and the Steptoe Canyon Fire near Clarkston continued to burn into this week.

Weather conditions in the drought-stricken Southwest helped spawn those storms. How does this happen?

Look no farther than the North American monsoon season, now underway in the Four Corners states of Arizona, New Mexico, Colorado and Utah, while seeping into parts of Nevada, Texas and California. Caused by a seasonal change in wind direction that triggers sporadic heavy rains and thunderstorms, it typically ramps up in July and persists until September.

While the rains can breathe life into parched landscapes and replenish streams and reservoirs, dry lightning storms are an unfortunate part of the package. This breed of thunderstorm develops much higher in the atmosphere than typical thunderstorms – as much as 10,000 to 15,000 feet above the surface. When conditions are warm and dry, the rain evaporates before it hits the ground.

That’s what happened on Wednesday morning of last week. Upper level winds carried monsoonal moisture more than 1,000 miles northward into our region, triggering high-based thunderstorms with plenty of lightning but little rain to dampen the ground. Consequently, dried vegetation was a prime source for ignition by lightning strikes.

Some cloudiness, sporadic light sprinkles and a rumble of thunder that moved into southeast Washington and parts of North Idaho early this week also originated from the monsoons.

As the heavy monsoon rains ease wildfire conditions in the Southwest, the level of flammability in the Inland Northwest remains high. Another monsoonal moisture surge could deliver more dry lightning to our region, resulting in more wildfires.

Fortunately, the National Weather Service keeps a sharp eye on the monsoon’s atmospheric developments and issues alerts and warnings before dry thunderstorms release their electric fury here in the Pacific Northwest. In the meantime, heat and drought conditions are forecast to continue in the Inland Northwest. The last two days of July, which are Friday and Saturday, are expected to be at or above 100 degrees, followed by temperatures in the low 90s the first week of August.

No big rain events are on the horizon.

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