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May heat wave scorches Pacific Northwest, sets new records

By Courtney Travis, Accuweather.com

Soaring temperatures over the past week have broken numerous record highs in cities across the Northwest.

AccuWeather meteorologists say that some areas could finally see relief in the form of cooler weather, but above-normal warmth is forecast to shift into other parts of the region.

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The unusually warm conditions began in the Pacific Northwest on Friday. Temperatures in Portland, Ore., peaked at 90 degrees Fahrenheit that day, hitting that mark for the first time this year. It was the first time 90 degrees F was observed in the city since Sept. 26.

The temperatures in Portland would continue to reach or surpass 90 degrees F through Monday, with the highest temperature of the heat wave of 93 occurring Saturday. Those temperatures are more akin to July or August, experts say. From Friday through Sunday, each high temperature set a new daily record for the day in Portland.

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Although Monday's temperature of 92 fell one degree shy of tying the daily record high of 93 from 2006, the afternoon high in the low 90s instead helped set a different record.

"This recent heat wave set a new record in Portland, Ore., for the number of consecutive days above 90 degrees during the month of May, bringing the tally to four," said AccuWeather senior meteorologist Heather Zehr.

The previous May record for consecutive days with temperatures above 90 was three from May 6-8, 1987.

Other cities across the Northwest broke daily high records this past week. From Friday to Monday, Seattle set four daily record highs in a row, peaking at 89 on Sunday. The high temperature of 88 degrees Monday broke the daily record high of 85 from 2007.

The Emerald City failed to reach 90 degrees during the period of unseasonable warmth, but reaching that feat would have been rather rare for May. It's been over a decade since Seattle reached that temperature threshold in May the last day of 90 degrees or higher there during the month was on May 17, 2008. Seattle's all-time highest recorded temperature during the month is 93 and was established on May 21, 1963.

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AccuWeather forecasters say that above-normal temperatures are expected to continue for the Pacific Northwest through the middle of the week. In most cases, the heat is unlikely to be as extreme as in recent days however, temperatures in Portland could again be in near-record territory through Thursday with temperatures forecast to settle near 90 degrees F in western Oregon.

By the end of the week, a notable change in the weather can be expected for the Interstate 5 corridor.

"Late this week, a large storm system swirling over the Pacific will approach the West Coast, allowing much cooler marine air to take the place of the heat near the coast," Zehr said.

Temperatures will fall from the low to mid-80s in Seattle on Wednesday into the low 70s by Saturday and even into the mid-60s by Sunday. In Portland, afternoon highs will go from the mid-80s, which is not far from record levels, to the low 70s Sunday.

"These forecast temperature readings, while quite the contrast from early week temperatures, will actually be close to historical averages in the coastal Northwest," Zehr added.

At the same time, this pattern change will push the area of high pressure responsible for the record heat inland, creating a warmup for interior parts of the Northwest.

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In Boise, Idaho, temperatures are forecast to reach the lower 90s Friday and Saturday which, if achieved, could tie or break the city's daily high temperature record of 90 Friday. Even without breaking the record, temperatures near 90 in the second half of May are about 15 degrees above the historical average for Boise.

Unlike the major cities closer to the Pacific Ocean, Boise has yet to reach 90 this month. However, the city did reach 90 degrees once earlier this year on April 30.

Bend, Ore., residents will also have to endure abnormally warm weather later this week. High temperatures are likely to reach the lower to middle 80s Thursday through Saturday, almost 20 degrees above the city's historical average.

By early next week, the cooler marine air from the Pacific is likely to infiltrate much of the Northwest, bringing temperatures back to more typical late-May levels, AccuWeather forecasters say.

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