Northwest US to experience surges of intense heat into this weekend

As heat slowly builds over the interior Northwest into this weekend with records poised to be set, waves of heat will be experienced along the Pacific coast into Saturday.

As major heat continues across much of the interior West well into the second half of July, intense heat will make its presence known in the Northwest as well, AccuWeather meteorologists say.

A northward bulge in the jet stream and a high pressure area will dominate the overall weather pattern for the western United States through this weekend, AccuWeather Senior Meteorologist Dave Houk said, "But as disturbances attempt to slice northward on the back side of the high pressure area, along the Pacific coast, temperatures will surge to high levels on some days before being knocked down briefly."

One such surge in temperatures occurred Tuesday, with highs in the upper 80s in Seattle and well into the 90s in Portland, Oregon. The same heat surge will cycle farther to the east, with less day-to-day variance over the interior Northwest into midweek with a high near 100 forecast for Spokane, Washington; and Pendleton, Oregon.

Temperatures will dip back close to the historical average Thursday along the Washington and Oregon coast before throttling up again from Friday to Saturday. Highs will trend back up through the 80s in Seattle and into the 90s in Portland, for example.

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Another slight cooldown will reach the coast and some areas just east of the Cascades later this weekend.

While it usually takes a stiff offshore breeze to counteract the influence of the Pacific Ocean along the Interstate 5 corridor to the immediate coast in the Northwest and bring record-challenging heat, multiple daily high temperature records may be toppled over the interior in the pattern.

Highs in Pendleton will be within a few degrees of 103 both Saturday and Sunday, while in Spokane the record of 103 set back in 1905 is forecast to be smashed with a high of 106 Sunday.

Farther to the east, Boise, Idaho, has the potential to hit 100 degrees or higher each day through Tuesday of next week. As the heat crescendos into early next week, temperatures on one or more days from this weekend to Monday may approach 110 degrees. The all-time record high is 111, set on July 12, 1898, and July 19, 1960.

Other interior Northwest cities such as Pocatello, Idaho; and Helena, Montana, may challenge high temperature records daily.

Each disturbance that travels along the edge of the jet stream bulge and the periphery of the high pressure area may grab enough moisture from the Pacific to produce spotty thunderstorm activity, Houk explained.

"However, many of the storms may bring little or no rainfall, but with the usual lightning strikes," Houk said, "Because of the mainly dry storms, the potential for lightning-induced wildfires will increase."

From summer to early fall, much of the Northwest experiences the least amount of rain of the year, and vegetation tends to dry out slowly in the sunshine and heat with each passing day. So when thunderstorms erupt, they often spark fires.

Close to 20 large wildfires were burning in Washington, Oregon, Idaho and Montana as of Tuesday, July 16, according to the National Interagency Fire Center. Multiple fires were burning over western and central Canada. Gov. Tina Kotek has declared a state of emergency over the threat caused by wildfires burning tens of thousands of acres throughout Oregon. Smoke from these fires will continue to lead to periods of poor air quality, with heat and light winds making matters worse.

While hiking is a popular activity for the Northwest in the summer, experts urge wilderness enthusiasts to closely monitor changing weather conditions and avoid being on treeless ridges -- a potential target for lightning -- when thunderstorms may develop in the afternoon hours.

The heat will tend to ramp up in the Southwest this weekend to early next week, but it probably will not be to the extremes of earlier this month.

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