Looming heat wave may lead to wildfire surge in Northwest

·5 min read

Another surge of heat is in the works for the northwestern United States, AccuWeather meteorologists say.  Not only will temperatures have the potential to approach levels set late last month, but the surging heat and widespread dry landscape could bring a significant uptick in wildfire activity.

"An upcoming heat wave for the Northwest this week could rival temperatures reached in some locations from late July," AccuWeather Long-Range Meteorologist Alex DaSilva said.

Temperatures are projected to surge from 5-10 degrees Fahrenheit above average early this week to 10-18 degrees or more above average beginning around the middle of next week.

The extreme heat will likely last until Saturday west of the Cascades, but it could persist longer across the interior Northwest, according to DaSilva.

During mid-August, typical highs range from the upper 70s along the Washington and Oregon coasts to the mid-80s over eastern Washington to the low to mid-90s over eastern Oregon and valleys of Idaho.

Many daily record highs for mid-August range from the mid-90s to low 100s in the Northwest and could be out of reach. However, there will be some records that could be toppled. Record highs of 88 in Seattle and 99 in Portland for Aug. 18 are still in the books from 1991 and 2016, respectively.

Overall, highs for this summer may be tough to match but are certainly possible, as the sun is not quite as intense as it was two weeks ago, DaSilva said. On the other hand, the ground is drier now and more responsive to sunshine than back in July. Depending on the strength of high pressure at both the lower and upper parts of the atmosphere, there is upward mobility potential with high temperatures for the region next week.

"Widespread highs at or above 100 are likely east of the Cascades to the lower western slopes of the Rockies for a several-day stretch later this week," DaSilva said.

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Temperatures peaked at 106 in Boise, Idaho, on July 31, while Spokane, Washington, topped out at 102 on July 29 and 31. Pendleton, Oregon, set a daily record high three days in a row from July 28-30, while the heat wave peaked at 111 degrees on July 29.

Meanwhile, along the Pacific coast, Seattle hit 95 all three days from July 29-31. The high temperature on the last day of the month set a record for the date. Highs in Seattle are likely to trend from the lower 80s early week to near 90 and perhaps well into the 90s by late week, forecasters say.

The upcoming heat wave will allow Seattle to add to its number of 90-degree days this year, which was already well above the average of four and had surpassed last year's total of eight. As of Sunday, the number of 90-degree days in Seattle was 10.

During the heat wave a couple of weeks ago, Portland, Oregon, reached the triple digits for three days and peaked at 102 on July 26 and 30. A daily record high was set on July 26. Highs from the middle to late parts of this week will range from the upper 90s to low 100s. Like Seattle, Portland was already ahead of its average of 15 90-degree days with 17 thus far and has the potential to surpass last year's number of 24 90-degree days this week.

Farther south and a bit farther inland, Medford, Oregon, peaked at 114 degrees and set a daily record high. Highs at or above 100 are in store for Medford, which is located west of the Cascades, from Tuesday through at least Friday. The city will continue to add to its number of 90-degree days through the upcoming weekend.

"Regardless of exactly how high temperatures get, there will be a surge in energy demands in the region," DaSilva said. "Many homes along the Pacific coast in the Northwest still do not have air conditioning, so heat waves can be more impactful than in other parts of the nation."

Prior to the late July heat wave, much of Washington, parts of Oregon and Idaho were coming off average to wet conditions, which helped to suppress wildfire activity at the time. However, that stretch of heat lasted eight days or more without any rain in some locations. The hot and dry conditions substantially dried out the grassy areas and brush in the region, and that has made the area more prone to wildfires, experts say.

The region has seen a surge in wildfire activity over the past couple of weeks. The largest fire in the region, called the Moose Fire, was located in central Idaho and had consumed over 77,000 acres and was a little over 27% contained as of Sunday.

"Dry weather and locally gusty winds during the new heat wave will elevate wildfire risk in general," DaSilva said.

A potential agitator to the increasing wildfire risk next week may be a disturbance in the jet stream that could swing northeastward. As a result of that ripple in the jet stream, forecasters say enough moisture from the Pacific and the southwestern U.S. could cause thunderstorms with little or no rain in some areas.

Lightning strikes from the storms could then spark new wildfires. The lightning storm risk will be greatest in portions of Oregon, Northern California and central and southern Idaho by late week. Clouds associated with this disturbance could also take the edge off the extreme heat in some locations.

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