'Dome of heat' to threaten many record highs across western US next week

By Jake Sojda, AccuWeather meteorologist

Updated May. 23, 2020 1:03 PM

After an unsettled and much cooler week for many in the West, the heat will be cranked back up to end the month of May.

Temperatures will begin the Memorial Day weekend hovering near or slightly below normal throughout much of California and the Desert Southwest. Farther north and east, high temperatures will range from 5-10 degrees below normal for most, with some of the coldest locations, from southern Idaho and western Wyoming into northern Nevada and Utah reaching as much as 15 degrees below normal Friday and Saturday.

For hikers trying to enjoy the holiday weekend in Yellowstone National Park, most of the park will be stuck in the 30s on Saturday with some accumulating snow. Higher points of the park could receive several inches by the time conditions dry out later Saturday.

The snowy scene captured by the National Park Service webcam at the Old Faithful Geyser in Yellowstone National Park Saturday morning.

However, by the holiday itself and throughout next week, the cooler weather of the past week will be a distant memory as warmth builds and record high temperatures are challenged.

"After a persistent southward dip in the jet stream during the past week, the jet stream will retreat northward, and a ridge of high pressure will set up, centered on the Southwest," said AccuWeather Senior Meteorologist Brett Anderson. "This will serve as a 'dome of heat' across the region next week."

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The "dome of heat" will gradually build through the weekend. By Sunday, most of the Pacific Northwest will be back to near-normal temperatures for the Interstate 5 corridor in Washington and Oregon. This means temperatures will range from the mid-60s, around Seattle, but farther south, in Oregon, the warmth will be above normal. AccuWeather forecasters are calling for temperatures in the mid-70s around Eugene while Medford could reach the 80-degree mark.

In the interior Northwest, while temperatures will be several degrees warmer on Sunday as opposed to Friday and Saturday, they will still remain around 4-8 degrees below normal. This translates to temperatures in the valleys from northern Nevada into western Montana in the 60s and low 70s.

By Memorial Day, most of the Northwest will be around or climbing above normal, with temperatures continuing to build throughout the week.

"By next Friday, most of the Northwest will be 15-20 degrees above normal," Anderson said. "A few locales could even approach 25 degrees above normal. Many records are likely to be set by the end of the week."

Next Friday, Seattle could reach 80s degrees. The record for the day is 85 set in 1973.

In the Southwest, the story will be similar, but the heat will build even faster. "While it will take until later in the week for the Northwest to really start feeling the heat, many in the Southwest will be sizzling already on Memorial Day," Anderson said.

Much of California will already be 5-10 degrees above normal for the holiday, with a few spots in Northern California pushing 15 degrees above normal.

"While most high temperature records aren't expected to be broken on Monday, a few locales in Northern California, like Redding and Sacramento, could come close," Anderson explained.

The records to beat on Monday are 98 in Redding and 100 Sacramento. The returning heat comes as much of Northern California and the Northwest are still suffering from severe drought.

"The brief switch to a cooler, wetter pattern last week will help in the short term, but overall, it did little to cut down on the moderate to severe drought conditions covering much of the Northwest," said AccuWeather Meteorologist and Western U.S. weather blogger Brian Thompson.

"The building heat will help to dry out what moisture was provided over the last week and raise the wildfire threat once again."

Tuesday through the end of the week is when the scorching heat will peak across California and expand across the rest of the Southwest.

Most of the region will be 10-20 degrees above average Wednesday through Friday. Downtown Los Angeles could reach the 90s on multiple days, while downtown San Francisco can reach the lower 80s. An average high for late May in downtown San Francisco is 65 degrees.

Locales surpassing the century mark will be common across interior portions of California. In the Desert Southwest, the mercury will soar into the 110s during the middle and end of the week.

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Late next week, Phoenix could challenge its all-time record high for the month of May of 114 degrees. The all-time record for any month in Phoenix is 122 degrees.

As of Saturday morning, excessive heat watches were already in effect for portions of the Southwest for next week. Check for updates at the AccuWeather Severe Weather Center.

Heading into June, AccuWeather meteorologists say the heat is expected to taper to more seasonable levels.

"The upper-level ridge will shift toward the Rockies and Plains, allowing for more cooling and onshore flow on the Pacific coast, and perhaps even the return of more clouds and showers in the Northwest" said AccuWeather Long Range Meteorologist Tyler Roys.

"However, temperatures in the Desert Southwest and much of the Rockies will still remain above normal," Roys added.

Keep checking back on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier and Verizon Fios.