Humidity, storms to surge in western US as heat eases in California
A pattern change will allow California to cool off a bit, but also cause drenching storms to erupt over the interior West.
On Sunday, temperatures soared to near-record levels above 100 F across California's interior.
However, the record-challenging heat will subside through midweek.
An area of high pressure shifting eastward will gradually cause temperatures to drop across interior California and then the remainder of the Southwest.
"The first to feel these changes will be California, when temperatures will start trending down on Tuesday," said AccuWeather Long-Range Meteorologist Max Vido.
The temperature difference will be noticeable in cities like Fresno, California; Flagstaff, Arizona; and Las Vegas. From their peak on Sunday and Monday, high temperatures will drop 5-15 degrees F by Wednesday afternoon.
Overall, temperatures across the state of California will be within a few degrees of normal by the middle of the week. Fresno, California, will reach the upper 90s in the afternoon, while Palm Springs returns to the lower to middle 100s.
An onshore flow off the Pacific Ocean will continue to keep it cool along the beaches of California.
"As the high continues eastward, the core of the heat will position itself over the Rockies by the middle of the week," Vido added.
Temperatures will trend a few degrees higher Tuesday and Wednesday for places like Santa Fe, New Mexico; Casper, Wyoming; and Denver.
The temperature swings in these locations are not expected to be quite as drastic as those across California, Nevada and Arizona.
Part of the reason for this will be the location of the high over northwestern Texas. The clockwise flow around the high will help to steer moisture from Mexico back into the Southwest. The increased moisture will lead to more clouds and even more thunderstorm activity, both of which will put a cap on the heat by blocking the summer sunshine.
After a break from widespread thunderstorms early in the week, a surge of moisture will once again bring the threat for flooding downpours.
This sort of pattern is common during the North American monsoon season, which generally occurs from June to September. The monsoon got a much later start than average this summer and did not kick into gear until mid- to late-July.
Thunderstorms will tend to blossom over the highest terrain during the afternoon hours and drift toward the lower elevations into the evening and overnight hours.
"In these thunderstorms, torrential downpours are possible in localized areas with as much as half an inch of rain in just a few minutes," according to AccuWeather Senior Meteorologist Alex Sosnowski.
"This type of rainfall on the arid terrain often leads to flash floods and mudslides," Sosnowski said. "Normally dry stream beds, called arroyos, can become raging torrents of water in a matter of minutes."
Hikers and motorists should keep an eye out for developing storms nearby.
Take care not to drive through a flooded roadway. It only takes 12 inches of water to sweep most vehicles away, and the water can disguise a washed-out roadway.
"Even if a particular area is directly missed by one of these thunderstorms, there is still a danger from a distance, where water can flow a dozen miles or more downhill through canyons and across secondary roads," Sosnowski said.
"Even in urban areas such as Phoenix, Las Vegas, Salt Lake City and Denver, enough rain can pour down to cause urban flooding in some neighborhoods with little notice."
Lightning can strike areas well away from where it is raining, posing a threat to those not directly being impacted from a thunderstorm's rain.
This expands the danger zone even farther from the storm, posing a risk for anyone who does not take shelter inside if they hear a rumble of thunder. If you are close enough to a thunderstorm to hear thunder, you are close enough to be struck by lightning.
Additionally, lightning strikes, where little or no rain falls, can also potentially spark a wildfire.
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