Monsoon Watch: Southwest Thunderstorm Season Kicks Into Gear

Jonathan Belles
Published: July 23, 2019

A pattern change across the Lower 48 has kicked the Desert Southwest monsoon's thunderstorm generator into gear early this week.

The driving factor of the monsoon in the United States is a ridge of high pressure that typically parks itself over the Rockies or Plains from summer into early fall.

Winds also increase from the east and southeast over northern Mexico and parts of the Southwest. This allows moisture from both the Gulf of Mexico and the Gulf of California to arrive in the Desert Southwest.

(MORE: 5 Things to Look for in the Southwest Monsoon

Setup for the return of monsoonal moisture.

This pattern change has not only ignited thunderstorms over the mountains of Arizona and New Mexico, but also in the low deserts, including the Tucson and Phoenix metro areas.

Current Radar, Satellite, Lightning Strikes

Thunderstorms with gusty winds rumbled through parts of Phoenix late Monday night. Blowing dust dropped visibility to a quarter mile or less near Queen Creek.

Davis-Monthan Air Force Base near Tucson clocked a wind gust up to 66 mph from thunderstorms on Monday.



Showers and storms will once again pop up during the afternoon hours in the higher elevations of Arizona, New Mexico and Colorado. A few storms could also make it into the lower elevations across the Southwest.

Tuesday's Forecast

Through the rest of the week, drier air may eventually push into Arizona and Southern California, but afternoon and evening thunderstorms may continue to rumble from the Sierra of California across Nevada and into Utah, Colorado and New Mexico.

(MAPS: 7-Day Forecast Highs and Weather

Precipitation Outlook

Most spots will receive less than a half-inch of rain, but a few mountainous locations in the southern Rockies and on Arizona's Mogollon Rim could get up to an inch or so.

A few spots could see localized flooding for short periods of time where the heaviest rain occurs.

Rainfall Forecast

These thunderstorms could also set off dust storms, otherwise known as haboobs, in parts of the Four Corners region.

The rain is expected to be beneficial for some across parts of New Mexico, where a stubborn drought is ongoing.

(MORE: Climate Change Will Make Droughts Hotter and Longer, NOAA Study Says

Setup for the Summer Monsoon

Although the dates for the summer monsoon may vary a bit across the region, the National Weather Service's Phoenix office has established some guidelines. One example is if the dew-point temperature is 55 degrees or higher over a three-day period. Also, there are occasional breaks in this pattern during the season.

The time period established for the summer monsoon is from June 15 to Sept. 30. The average onset of the monsoon in Phoenix is July 7.

Prior to the onset of the monsoon (generally late May and early June), temperatures across the Desert Southwest are extremely hot and humidity levels are quite low. That changes as we move into July and August, persisting into September.

In late June and early July, a ridge of high pressure commonly sets up over the Four Corners area (where Colorado, New Mexico, Utah and Arizona come together). Low pressure (a thermal low) develops across interior areas of Southern California, and a southeasterly flow of moist air is transported into the region.

This has already been one of the drier starts to the summer thunderstorm season in southeastern Arizona and a much drier start than 2018 in northern Arizona, the NWS noted.

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