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Hot pattern to swell over much of Lower 48 this weekend

An early summer heat wave will bring temperatures about 10 degrees above normal for much of the U.S.

High temperatures predicted Saturday by the National Weather Service.

Summer is here, and the atmosphere knows it. A sprawling dome of heat will park over the United States next week, bringing highs topping 90 degrees to 130 million Americans and triple-digit temperatures to some.

It will feel even hotter because of soaring humidity in the East, while the same dome of heat saps the West of moisture and bolsters late-season wildfire concerns. The core of the heat could eventually become centered over the Great Lakes as the massive ridge of high pressure spans coast to coast.

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The first signs of the fledgling heat dome were already emerging in the West, where strong high pressure was bringing temperatures over 100 to the Central Valley of California and interior Washington State earlier in the week. Heat advisories blanketed the Columbia River Valley region, and the harshest temperatures have since expanded east.

Bismarck, N.D., is expected to hit 101 degrees Friday, with widespread hundred-degree readings across the Dakotas. That could be a new daily record for Bismarck, beating out the 95 degrees observed in 1988. It will probably nab a record Saturday, too, with a projected high of 97 degrees.

Billings, Mont., was predicted to hit 99 on Friday, while Casper, Wyo., and Boise, Idaho, hover in the mid-90s. The former could break a record. Salt Lake City is under an excessive heat warning for “dangerously hot conditions with temperatures around 100.” It hit 97 on Thursday, establishing a record. A record will probably be set Friday.

Phoenix and Las Vegas could approach 110 degrees, while Death Valley hit 120 degrees for the first time this year Thursday.

Accompanying the heat is a concern for wildfires. Red flag warnings for fire danger are up for central Washington, Oregon and Northern California on Saturday, where lingering heat will combine with single-digit relative humidity values and winds gusting up to 40 mph to bring an increased risk of wildfire ignition and growth.

Red flag warnings have also been issued in Montana, North Dakota and northern Minnesota, as well as in Utah. It marks the start of a long and likely significant wildfire season for the West, worsened by prolonged “extreme” to “exceptional” drought, a significant deficit in soil moisture resulting in dry vegetation, and the expectation that anomalously hot temperatures — due in part to human-induced climate change — will persist into the fall.

California facing drought crisis as water shortages mount and fire danger escalates

Heat builds east this weekend

Over the weekend, the instigating ridge of high pressure and its associated warmth will flatten and expand eastward, draping a swath of heat, some significant, over most of the continental U.S. An exception may be areas around East Texas and the Gulf Coast where temperatures will be closer to normal due to a weakening eddy of low pressure that could bring clouds and storms.

On Saturday, Chicago will climb into the 90s, as will D.C. Boston and New York will approach 90, too. In Minneapolis, Saturday’s high is forecast to reach 98, which would crush the existing record of 92 degrees from 1925 and 1911.

The nation’s capital could make it into the mid-90s on Sunday, when highs of at least 90 cover much the eastern half of the nation.

By Monday, much of the United States will see elevated temperatures, though a disturbance will also be working ashore in the Pacific Northwest, bringing unsettled conditions near the coast.

There are signs that the core of the heat could become established over the Great Lakes toward the middle of next week, with unseasonable warmth likely for just about everyone east of the Continental Divide.

The heat could also brew strong thunderstorms, particularly along the northern periphery of the high pressure dome where warm, moist air meets jet stream energy and cooler air banked up in Canada. “Ridge runners” have a tendency to travel long distances, and mix strong winds from the upper levels down to the surface.

It’s unclear where and when such storms will brew, but right now there are signs that thunderstorms could visit the northern Plains between June 8 and June 10 and again from the 12th onward. Some may be strong to severe.

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Storms of the ridge-runner variety, meanwhile, are most pronounced when mid-level flow is westerly or northwesterly; that means northern New England could get a few ridge runners next week, but otherwise the Northern Tier and North Central U.S. may have to wait until the dome of heat occupying the nation settles south a bit before storms reenter the forecast.

Looking ahead, NOAA’s Climate Prediction Center is calling for near or above-average temperatures to predominate nationwide through the entirety of summer.