Monsoon momentum: More of Southwest US braces for thunderstorms

Thunderstorms have been a frequent flyer in parts of the Southwest and just about non-existent in other portions of the region. However, that will soon change.

Summertime conditions have allowed parts of the southwestern United States to experience locally drenching and gusty thunderstorm activity, but storms have been scarce from western Arizona and Nevada to California thus far. However, AccuWeather meteorologists believe that may change as the calendar turns to August.

Thunderstorm activity from New Mexico to southern Colorado, westward to eastern Arizona, and parts of Utah has been average to fruitful so far this summer. For example, in Durango, Colorado, 4.08 inches of rain fell from June 1 to July 22, which is 3.32 times the historical average. Albuquerque, New Mexico, has received 3.01 inches of rain during the same period, which is 1.8 times the historical average.

The annual flip of the wind from the west to the southeast, known as the North American monsoon, brings in enough moisture from the tropics to raise humidity levels, which helps trigger thunderstorms over much of the western U.S. in the summer.

The extent of the monsoon and its thunderstorms varies from year to year and location to location. This season, AccuWeather's long-range team of meteorologists expected a decent amount of storms from the southern Rockies to part of the Great Basin but limited or delayed activity farther to the west. This has been the case thus far, and there are signs that some storms may soon propagate farther to the west.

"It's really all about the position of high pressure over the western United States," AccuWeather's Lead Long-Range Meteorologist Paul Pastelok said.

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"We expect the center of this high pressure area to slide from its more southern position in the West now to an area farther to the north," Pastelok explained, "This will remove the block of moisture currently in place over the Southwest and create more of a southeasterly breeze, which will help direct existing moisture to the east into more of the Colorado River Basin and California."

Pastelok adds that this will likely begin in late July to early August.

"The result will not only be an uptick in thunderstorm activity over the higher elevations in California, Nevada and western Arizona, but also some thunderstorms for the intermediate and even lower elevations, including interior California," Pastelok said.

There is thunderstorm potential in early August for a number of areas in the Southwest that have not experienced one yet.

Even though Las Vegas only typically picks up 0.30 of an inch of rain from June 1 to July 22, the desert city has received less than 0.10 of an inch. Yuma, Arizona, has only had a few drops of rain during the same period, compared to 0.18 of an inch for a historical average.

"The thunderstorm activity will not only bring with it the potential for a bit of rain in some areas that have not received any since the spring or winter with some soil dryness relief, but it will carry some risks to lives and property as well," Pastelok said, "Some of the storms may bring lightning-induced wildfires, winds strong enough to create vast dust storms and perhaps enough rain to bring flash flooding."

It does not take a huge amount of rain to trigger a flash flood in the arid, rugged terrain in the Southwest, especially through some of the canyons and arroyos (dry stream beds). Hikers should closely monitor thunderstorm activity as a storm, even several miles away uphill from their location, can trigger a flash flood.

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