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When will the record-breaking heat end in the western US?

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Numerous record-high temperatures were set across the western United States last week as dangerous heat built across the region. This heat wave, along with the risk of wildfires, will continue for much of this week.

"The recent hot weather across the western United States will remain as such for the next several days," AccuWeather Senior Meteorologist Matt Rinde said.

Seattle; Portland, Oregon; Boise, Idaho; Reno and Las Vegas, Nevada; Fresno, California; and Phoenix, Arizona, are just some of the cities that broke record highs on one or more days last week.

This week, the heat will continue to sit across the region, but will take a slow shift eastward throughout the week.

"A dip in the jet stream will approach the West Coast and trend high temperatures downward throughout the week," Rinde said.

The jet stream, which peaked along the West Coast this past weekend, leading to record-breaking heat, will shift into the Intermountain West into midweek, leading to a gradual cooldown of temperatures.

The jet stream is a narrow zone of strong winds in the upper levels of the atmosphere that separate the warmer air to the south and the cooler air to the north.

The sharpest cooldown will take place across Washington and Oregon. Highs from Seattle to Portland will trend from the 90s to near 100 F last weekend to the 80s F early in the week and the 60s F by the end of the week.

The dip in the jet stream will also lead to an onshore flow of winds along the West Coast beaches and locations within 20 miles from the coast, keeping temperatures in the 60s F and 70s F. This includes the major cities of San Francisco, Los Angeles and San Diego.

Highs across the Central Valley of California will dip from the triple digits this past weekend into the 80s F and 90s F.

Nonetheless, dry weather will be beneficial for any outdoor activities along the West Coast this week, such as golfing, swimming or attending a minor or major league baseball game.

As the heat slowly fades along the West Coast, the heat across the Intermountain West will peak by midweek.

"Across the Intermountain West, the heat will persist all week and will not relax until the upcoming weekend," AccuWeather Meteorologist Michael Doll said.

This includes Boise, Idaho; Salt Lake City; Billings, Montana; and Albuquerque, New Mexico.

"On Wednesday, Boise could break their record high of 96 degrees Fahrenheit, set just last year," Doll said.

"Anyone needing to go outdoors during the heat of the day should drink plenty of water, wear light-colored and loose-fitted clothing and take frequent breaks in the shade," AccuWeather Meteorologist Renee Duff said. "Those without air conditioning can seek relief from the extreme heat at local libraries, malls and designated cooling centers."

During the week, daily showers and thunderstorms will pop up across the Intermountain West. Should any lightning bolt strike the dry ground, a wildfire could ignite. Gusty afternoon winds could also spread any new or existing fire.

The heat from this past week left to the development of the Old Fire across Southern California which is now 80 percent contained as of Sunday evening.

At least six other wildfires are currently ongoing across the West, according to the National Interagency Fire Center.