While an uptick in moisture will lead to some much-needed relief from the recent extreme heat in the Southwest U.S., thunderstorms could also produce dust storms and dangerous lightning, AccuWeather experts warn.
Published Jul 27, 2023 11:57 AM EDT | Updated Jul 30, 2023 12:11 PM EDT
The return of showers and thunderstorms in the western United States has already ended one record-long streak related to the extreme heat in Phoenix, and will threaten another round this weekend, AccuWeather forecasters say.
The rain chances come courtesy of the return of the annual North American monsoon, which will pump moisture north from Mexico for at least the better part of the next week. While this year's monsoon has started off fairly weak compared to other years, it will produce just enough cloudiness and scattered rain to provide some welcome relief from the current extreme heat wave.
For the Phoenix area, some of that relief has already arrived.
"On Thursday morning, the temperature at Phoenix finally dipped below 90 degrees for the first time since July 9th," said AccuWeather Senior Meteorologist Heather Zehr. "A gust front rolled through and eventually knocked the mercury down as low as 88 degrees."
The gust front that ended the run of low temperatures at or above 90 in the city was produced by a nearby thunderstorm, which kicked up the wind and dust and allowed temperatures to fall. That 16-day run of morning low temperatures in the 90s was more than double the previous record of seven consecutive days that occurred three other times in 2020 and 2012; it also included an all-time record highest low temperature of 97 on July 19.
There is another active heat streak in Phoenix that will be jeopardized by the monsoon moisture this weekend: the run of days with a high temperature at or above 110 degrees. The streak began back on June 30, and has long since surpassed the previous record-long run of 18 days from the summer of 1974.
It may take until Monday for that run to end, however, as the monsoon moisture will only slowly ramp up over the next several days.
Thunderstorms will be isolated in nature through the remainder of the weekend. After that, the monsoon moisture will intensify, which will result in more widespread shower and thunderstorm activity and a relocation of the persistent heat dome farther east, say AccuWeather meteorologists.
The AccuWeather forecast for Phoenix calls for a high temperature below 110 degrees for the first time in about a month on Monday, a trend which will continue through this week thanks to an increase in cloudiness and thunderstorm activity.
As the thunderstorms bubble up each afternoon before fading late each evening, a reduction in temperature will not be the only change that they will bring. AccuWeather forecasters are also warning of some hazards from the storms in the coming days for those spending time outdoors or traveling.
Lightning can be frequent in these storms, with or without rain, and can create wildfires and pose a serious threat to those far away from substantial shelter. Additionally, downpours from thunderstorms can lead to flash flooding that can strand vehicles and lead to mudflows.
FILE - With Chase Field, home of the Arizona Diamondbacks baseball team in the background, a digital billboard updates the time and temperature as temperatures are expected to hit 116-degrees July 18, 2023, in Phoenix. President Joe Biden plans to announce new steps to address the extreme heat that has threatened millions of Americans, most recently in the Southwest. (AP Photo/Ross D. Franklin, File)
The downpours produced by monsoon storms can occur suddenly and violently kick up the wind, sending out waves in each direction that can create dust storms. These storms can quickly lower visibility, imperiling travelers on roads and delaying flights.
On Wednesday, numerous thunderstorms produced blowing dust and damaging wind gusts in the 50- to 70-mph range across the Phoenix and Tucson metropolitan areas.
Monsoon storms, heat relief will extend well beyond Phoenix
Arizona will not be the only beneficiary of the heat-reliving moisture, say AccuWeather forecasters.
"Monsoon moisture will shift westward into Monday into Southern California, underneath the persistent heat dome," added Zehr. "This will bring rain chances into at least the deserts of California and perhaps the mountains to the north and east of Los Angeles and San Diego."
The storms could then spread north into the Sierra Nevada of California and Nevada from Monday into Tuesday, says Zehr.
In Las Vegas, there hasn't been measurable rain since June 16, but that dry streak could end this week, along with a run of 100-degree high temperatures that dates back to June 30, the same day that Phoenix's run of 110-degree highs began.
Outside of Arizona, California and Nevada, more of the Intermountain West from New Mexico to Idaho will experience an uptick in daily thunderstorm activity and a drop in temperature this week.
"Temperatures in most of the interior Southwest will drop closer to historical averages beginning this weekend," said Zehr. "The cooler temperatures look to have staying power through at least the early part of August."
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