Air conditioners can be given a break and jackets and umbrellas will be needed for some as the coolest air since late May and early June grips the western United States into midweek.

“September got off to a hot start across much of the West, but afternoon highs will be 10-20 degrees Fahrenheit lower in most areas early this week compared to last week,” AccuWeather Senior Meteorologist and western U.S. blogger Brian Thompson said.

One wave of cool air pushed through the Pacific Northwest with locally heavy thunderstorms at the start of the weekend. In Seattle, lightning forced a delay during the NCAA football game between the California Golden Bears and Washington Huskies.

 A reinforcing shot of cool air will spread through the Western states during the first half of this week, bringing relief from intense heat, even to the desert areas of the Southwest.

“Phoenix has not had a high temperature below 95 since May 29, and that streak may be broken in this cooldown,” Thompson said.

Temperatures in Las Vegas are expected to dip into the lower 90s by Tuesday and Wednesday, which is about 5 degrees below average.

Dry, gusty winds sweeping in as temperatures are trimmed can create travel difficulties for motorists, especially high-profile vehicles, while elevating the risk of new wildfire ignition and spread.

Farther north, clouds and wet weather underneath the core of the cool air will put a damper on the wildfire threat.

Highs in the 60s and 70s, which are 10-15 degrees below normal, may have people grabbing for extra layers before heading out the door in places such as Salt Lake City; Medford, Ore.; Spokane; and Missoula, Mont.

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