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Dangerous heat wave looming for Pacific Northwest

Excessive heat watches and red flag warnings were in effect across the northwestern United States Wednesday as record heat began building in some places and AccuWeather forecasters along with local officials are warning that the weather is going to become a lot hotter in the coming days.

"We're going to be looking at all-time record highs in some spots," AccuWeather Chief Broadcast Meteorologist Bernie Rayno warned for a part of the country where air conditioning is not a staple in homes. Rayno said some of the places that will see temps soar farthest above normal include those along the Interstate-5 corridor between Seattle and Portland.

Indeed, Seattle Mayor Jenny Durkin this week issued guidance outlining ways for residents to stay cool during the unusual warm spell. And the National Weather Service (NWS) office in Seattle provided tips for keeping homes that don't have air conditioning cool during a heat wave.

It is not just the northwestern U.S. where all-time record highs may be set. There is the potential for a new Canada high temperature mark to be set with the heat wave this weekend to early next week. That temperature is 113 F or 45 C and was set on July 5, 1937, at Midale and Yellow Grass, Saskatchewan.

"Kamloops, Kelowna and Lillooet, British Columbia, all have a shot at reaching or slightly exceeding the all-time Canada high temperature mark," AccuWeather Senior Meteorologist Brett Anderson said.

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Part of the Northwest got a little taste of the extreme heat on Monday, which was the first full day of summer. Several daily high-temperature records were set or challenged in western Washington and Oregon.

The temperature in Portland, Oregon, soared to 97 Monday and broke the old record of 96 set in 1992. Meanwhile, in Vancouver, Washington, the temperature shattered the old record of 91 set in 1938 with a high of 95.

Seattle just missed its first 90-degree reading of the season Monday, but then the heat backed off and the temperature didn't even reach 80 on Tuesday or Wednesday. However, people in the city will likely not have much longer to wait to hit the 90-degree mark this summer.

As a weak storm system pushes slowly inland from the Pacific Ocean into Thursday, temperatures will be held back temporarily in coastal areas of the Northwest.

The slight cooldown will trim temperatures back to 5-10 degrees above average into Thursday, before a shift in the jet stream is expected to turn the atmospheric furnace on high Friday, Saturday and Sunday.

Average highs this time of year range from near 70 in northwestern Washington to the mid-70s along the Oregon coast and eastern Washington to near 80 along in far eastern Oregon along the Idaho border. Seattle's high temperatures will be in the upper 70s to near 80 Wednesday and Thursday, while temperatures in Portland will reach in the mid-80s into Thursday. It will be a tad warmer, with highs registering in the upper 80s in Spokane the next few days.

On this image, captured on Tuesday morning, June 22, 2021, a swirl of clouds associated with a weak storm can be seen off the California coast with bubbly clouds associated with spotty thunderstorms over Oregon. (CIRA at Colorado State/GOES-West)

The weak storm system and an associated dip in the jet stream will set up shop over the interior Southwest late this week and this weekend. In that position, a little edge may be taken off the heat in the Southwest, where triple-digit temperatures have been common with some record daily highs falling by the wayside this June.

With the jet stream forecast to bow southward over the Southwest, temperatures there may be suppressed just a bit. On Wednesday, Las Vegas recorded a high of 96 degrees Fahrenheit, which is the first time the city has failed to reach 100 since June 11. Temperatures in the upper 90s are forecast there again on Thursday.

"As the jet stream dips southward over the Southwest, a compensating pattern will result in an intensifying northward bulge in the jet stream from Friday through Sunday in the northwestern U.S. and part of southwestern Canada," AccuWeather Meteorologist Alyssa Smithmyer said.

When the jet stream behaves this way the air at mid- and upper levels of the atmosphere become very warm. When the air upstairs in the atmosphere is warm, the air down near the ground has a much easier time heating up, especially in the summer when ground conditions are dry.

The upcoming pattern for the Northwest and the southern part of British Columbia is forecast to set more daily record high temperatures. Highs in the 90s and even low 100s are likely to be common.

"Locations across central Washington, such as Yakima and Omak, are forecast to touch the low 100s on Friday," Smithmyer said.

"During Saturday and Sunday, forecast high temperatures upwards of 100 degrees will spread across a large area in Washington, Oregon, Northern California, Idaho, Oregon, and western Montana," Smithmyer continued.

Highs in Portland are forecast to surge well past 100 on Saturday, Sunday and Monday. The record of 102 set in 2006 on Saturday and record of 98 set in 2000 on Sunday are expected to be blown away. The forecast high of 106 on Sunday in Portland is just one degree shy of the all-time record high of 107 set on multiple dates in July and August, reached most recently during the summer of 1981.

Meanwhile, not only will Seattle reach the 90-degree mark for the first time this season in the pattern, but record highs are forecast to be blown away. The high on Saturday in Seattle is forecast to be in the neighborhood of 96, which will easily surpass the old record of 90 set in 2006. On Sunday, the temperature is predicted to top 100 in Seattle and smash the old record of 92 set in 2015. Another record-breaking 100-degree day is forecast on Monday in the city.

Seattle and Portland are not the only locations that will be challenging record highs this weekend. Other cities such as Spokane, Washington; Missoula, Montana; Redding, California; Vancouver, British Columbia; and Eugene, Oregon, will all make runs at record highs on one or more days. On Sunday, The Dalles, Oregon, is forecast to come within 1 degree of the all-time record high of 112 set on July 20, 1956.

If the Spokane International Airport hits 100 on Saturday, it will be tied for the 3rd earliest date to hit 100 since 1881, according to the National Weather Service.

AccuWeather RealFeel® Temperatures will be several degrees higher and can surpass 110 in some locations during the afternoon hours.

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While athletes making their runs to qualify for the U.S. Olympic Team at Hayward Field in Eugene will get a little break from the extreme heat through Thursday with highs forecast to be in the upper 80s, temperatures are forecast to trend upward from Friday through Sunday. Highs are predicted to soar into the lower 90s Friday, the upper 90s Saturday and near 100 Sunday.

Excessive heat watches (dark red), excessive heat warnings (magenta) and red flag warnings (red) were in effect through Wednesday.

On Monday, the temperature climbed to 95 at Eugene and just missed tying the record high of 96 set in 1992, AccuWeather Senior Meteorologist Paul Walker said.

"Temperatures on the track were near 100 degrees during Monday evening," Walker said.

"Little reprieve from the heat is likely for at least the first part of next week across the northwestern U.S. and southwestern Canada, as a dome of high pressure is expected to remain anchored over the region," Buckingham said.

While the number of people with air conditioners has increased in recent years in the Northwest and particularly in Washington and Oregon according to data from the U.S. Department of Labor, based on HVAC installations, not every resident has that means of keeping cool.

People without air conditioning are urged to avoid strenuous activity and remain hydrated. While fans can be an effective means of reducing body temperature by evaporating perspiration, they can accelerate dehydration in some cases.

"As a result of the persistent heat and high energy demands this month, residents that do have air conditions and make use of their means to keep cool can expect costly electric bills," Buckingham said.

Snowmelt over the high country will have streams and rivers running high, fast and cold. There is still snow on some of the mountaintops, and as temperatures rise, so do freezing levels. Melting snow can cause flooding as creek and river levels rise.

The extreme nature and duration of the heat can cause roads to buckle and rails to bend, which can pose hazards for motorists and freight and passenger train operators.

Wildfire risk on the rise

Much of the West has been suffering from building drought this year with expanding areas of exceptional dryness that has some reservoirs at record low levels for so early in the season. The drought has prompted fears of a very bad fire season and has officials taking precautions to avoid water shortages.

Even though there are hopes that showers and thunderstorms produced by the North American monsoon will provide some temporary relief for part of the Southwest this summer, with such widespread heat and drought so soon, the stage could be set for a record-challenging year for wildfires in the western U.S.

"The early extreme heat and dryness will only accelerate the drying-out of vegetation this summer," Buckingham stated.

Heat and drought will continue in the West, and late summer and early autumn prime wildfire season is on the horizon.

The 10 years with the greatest amount of acreage burned in the U.S. have all occurred since 2004, with the years 2015, 2020 and 2017 at the top of the list respectively, according to data from the National Interagency Fire Center.

As of June 22, 2021, 1,118,377 acres have burned thus far this year. On a scale from 1 to 5, the National Preparedness Level (PL) was at a 4 on Tuesday. Since 1990, June 22, 2021 was the second earliest the level had increased to PL4. The level has only reached a PL4 three other times during the month of June in the last 20 years, including in 2002, 2008 and 2012.

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