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Wetter-Than-Normal Monsoon to Aid US Desert Southwest

By By Kristina Pydynowski, senior meteorologist
July 14, 2015, 9:49:08 PM EDT

The monsoon season started earlier than normal and will yield above-normal rainfall, both of which will spell drought relief for the United States' Desert Southwest.

The 2015 monsoon season officially started on June 25 in Tucson, Arizona, according to the National Weather Service, then commenced in Phoenix the following day. On average, the monsoon waits until early July to start in both cities.

June 2015 ended as Arizona's second wettest June on record with above-normal rainfall across the rest of the Four Corners states, NOAA reported.

That will be the theme going forward through the rest of monsoon season, which typically runs through the end of September.

"I think that with a well above-normal hurricane season expected in the eastern Pacific Ocean that there is a higher chance than normal for big tropical injections [into the Desert Southwest] through the summer and early fall," stated AccuWeather Western Weather Expert Meteorologist Ken Clark.


"This could continue to cause wetter-than-normal weather in Arizona, far southern and eastern Nevada, Utah, Colorado and even parts of New Mexico (especially western areas)," Clark added.

The arrival of tropical moisture can enhance monsoonal thunderstorms in the Southwest in less than two weeks.

"Tropical moisture from the eastern Pacific may work into the Desert Southwest around July 18 to 20," stated Chief Long Range Meteorologist Paul Pastelok. "The greatest potential for heavy thunderstorms and flooding from this event would be around Arizona."

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"Some drenching thunderstorms can even get into southern California, especially the deserts," Pastelok continued.

Prior to July 18, monsoon thunderstorms will generally be centered over the Four Corners with moisture occasionally leaking to Montana and the Sierra. The afternoon and evening hours will be most active, as is typical.

Throughout monsoon season, any thunderstorm can trigger localized flash flooding, frequent lightning and occasionally damaging winds depending on the situation. However, above normal rainfall is needed to ease the region's long-term drought.

In its most recent release on Thursday, the United States Drought Monitor reported that parts of Arizona, Utah, far western New Mexico and eastern Nevada continued to suffer from a severe drought.

More than 70 percent of California remained in an extreme to exceptional drought, but significant drought relief and the frequent thunderstorms from the monsoon will remain focused on places to the east.

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It is not out of the question for showers and thunderstorms during this monsoon season to drift to California's Central Valley or the Los Angeles Basin, depending on the wind direction. That will not happen often.

Despite the Central Valley or Southern California missing out on most of the thunderstorm activity, monsoon moisture could still aid with the region's water supply.

"Since many of the streams and rivers leading out of the Sierra go into reservoirs, an increase in [thunderstorm] activity even over the Sierra might help the reservoir levels a bit," Clark added.

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