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Big cooldown to end lengthy warm spell in Pacific Northwest later this week

By Kyle Elliott, AccuWeather meteorologist
June 19, 2019, 2:29:13 PM EDT

After record-breaking heat baked the Pacific Northwest last week, a large-scale shift in the weather pattern will bring big changes to the region later this week.

Through Tuesday, high temperatures in Seattle and Spokane, Washington; Portland and Bend, Oregon; and Boise, Idaho, while not as extreme as last week, were still between 5 to 10 degrees Fahrenheit above average.

However, a cooldown, that began on Wednesday, will become more pronounced by Thursday.

By the latter half of the week, a large dip in the jet stream will squash the ridge of high pressure that has been promoting the prolonged stretch of unseasonable heat in the Northwest.

A storm system diving into the Northwest and northern Rockies will drag cooler air southward out of western Canada, and highs by late week will be 25 to 35 degrees lower than what they were during the peak of the heat wave.

NW Cooldown

After the temperature in Spokane, Washington, hit 85 on Monday, highs will struggle to reach the lower 60s F on Thursday.

Similarly, highs in the mid- to upper 60s F in Portland on Thursday will contrast Monday's high of 81.

Even in the Snake River Valley of Idaho, high temperatures may fail to reach the 70-degree mark on both Thursday and Friday.

For most, temperatures late this week will end up 5 to as much as 15 degrees below normal, forcing residents to trade in sunglasses, shorts and swimwear for sweatshirts, jackets and jeans.

Gusty winds, mainly cloudy skies and hit-or-miss showers will accompany the late-week cooldown, making it feel even chillier than the thermometer might suggest.

Although most valley locations should remain rain-free this week, daily rounds of showers can be expected in the higher elevations. In some cases, snowflakes may mix in with the rain on the highest peaks.

There could even be patchy frost in the mountains on Thursday and Friday mornings, so anybody with hiking or camping plans should be sure to pack rain gear and warm, layered clothing so as to lessen the risk for hypothermia.

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In addition, the strong winds accompanying the storm system will greatly increase the risk for wildfire development and spread. A surplus of precipitation over the winter and spring has led to explosive vegetative growth in the West, but the recent dry spell has allowed the soil and this vegetation to dry out quickly.

Any spark could quickly ignite and explode into a large wildfire with the vegetation in the Pacific Northwest, basically serving as a tinder box for the rest of the summer.

The fire risk will expand into progressively higher elevations as snow melts and vegetation dries out.

People are urged to extinguish campfires and cigarette butts after use. Although lightning accounts for a small percentage of annual wildfire ignition, a much larger percentage of wildfires are sparked through human means.

By the weekend, the storm system will lift northeastward into southern Canada and allow more seasonable air to return to the Northwest. However, a return of the unseasonable heat of late is not foreseen through the end of June.

Download the free AccuWeather app to see just how cool it will get in your location late this week. Keep checking back for updates on and stay tuned to the AccuWeather Network on DirecTV, Frontier and Verizon Fios.

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