Seattle, Portland could reach 90 degrees this weekend as a spring heat wave builds across Northwest
Much of the month of May so far has been unusually cool and damp across a large swath of the western United States, but AccuWeather forecasters say a major pattern shift is on the way for the region. Dozens of high-temperature records will be in jeopardy this weekend and into next week as the West begins to sizzle.
An early springlike chill will persist across the West through the middle of the week as a significant dip in the jet stream remains in place. High temperatures in cities like San Francisco and Medford, Oregon, continued to fall short of historical averages on Wednesday, with respective highs of 59 and 71 F.
By Thursday, it will feel like Mother Nature flipped a switch as the jet stream begins to bulge northward across the Western states.
"An unusually strong upper-level area of high pressure will pump up the heat as it builds into the Northwest later this week," AccuWeather Senior Meteorologist Heather Zehr explained.
This area of high pressure in the upper levels of the atmosphere will strengthen throughout the weekend and lead to a potent heat wave.
"It will have quite a bit of staying power as it holds on through early next week," Zehr added.
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Cities like Portland, Oregon, will begin challenging records by Friday as temperatures approach the mid-80s F. For mid-April, historical average high temperatures in the city usually hover around 69 degrees Fahrenheit.
The mercury will climb even higher Saturday as Portland approaches the 90-degree mark, challenging a daily record high that has stood for 50 years. In fact, both the Friday and Saturday daily high-temperature records in Portland have been in place since 1973.
By Sunday, Portland will sizzle as temperatures skyrocket into the lower 90s. Typically, the city encounters its first reading of 90 or more in the middle of June. The earliest day on record above 90 degrees for the area occurred May 6, 1987. While this weekend's heat may be too late to break that record, the proximity to a record demonstrates just how unusual of a pattern is expected.
Record-challenging heat will continue Monday as high temperatures remain in the upper 80s.
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Farther north in Seattle, record-challenging heat will hold off until the start of the weekend. AccuWeather forecasters say high temperatures in the Emerald City Saturday will hover around 80 degrees and will jump to 90 by Sunday.
Sunday and Monday look to be record-breaking days for Seattle with daily record highs of 88 from 2018 and 85 from 2007, respectively, in great danger of being overwritten.
Since high temperatures in the 90s are possible on both Sunday and Monday, the city will have at least two opportunities to rewrite history and secure the earliest 90-degree day on record. Currently, the earliest 90-degree day on record for Seattle is May 17, 2008.
"Temperatures may ease away from records toward the middle of next week, but they will remain well above historical averages for most, if not all, of next week," Zehr cautioned.
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As the Northwest heats up this weekend, AccuWeather forecasters say a different hazard will return to the Southwest.
At the end of the weekend, a portion of the jet stream is set to bulge back westward over the Southwestern states. This expansion will allow moisture from the center of the country to work its way west.
"The increase in moisture across the Southwest will keep temperatures in the area from reaching the same record heights as their counterparts to the north," AccuWeather Meteorologist Reneé Duff said.
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Even though the moisture will work to even out temperatures across the area, it'll come at the cost of storm development. Showers and thunderstorms may come to life over the weekend and into early next week, especially across the higher elevations of the Southwest.
Any heavier storm could lead to flash flooding issues, as rain may plummet to the ground faster than the soil can absorb the moisture. Lightning strikes from any thunderstorms can also pose a danger to anyone with outdoor plans, forecasters say.
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