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    Risk of wildfires, poor air quality to increase in western US as heat builds

    By Alex Sosnowski, AccuWeather senior meteorologist
    August 24, 2017, 3:06:15 PM EDT

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    Temperatures will again be on the rise over much of the western United States this weekend into early next week, increasing the wildfire threat and lowering air quality.

    "The upcoming surge of heat will not be as extreme as the heat wave of late July and early August, but will be noticeable given the more seasonable air of late," according to AccuWeather Meteorologist Renee Duff.

    Following a push of cool air and spotty thunderstorms in the Northwest into Friday, highs will trend upward.

    This weekend, highs in the 90s F to near 100 are projected for eastern Oregon and southern Idaho. Afternoon temperatures will approach or exceed 90 in Portland and 80 in Seattle.

    Static West Heat

    Heat will build over the Southwest as well.

    "Temperatures over the interior valleys of California will reach the triple digits this weekend, especially on Sunday," according to AccuWeather Meteorologist Maggie Samuhel.

    A light flow of air from the interior to the coast will also push temperatures upward. Highs near 90 are forecast for downtown Los Angeles this weekend.

    "The pattern may limit the extent of morning low clouds to just the immediate beaches," Samuhel said.

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    The combination of sunshine, light winds and hot air will lead to deteriorating air quality due to existing wildfires in the region and major metro area pollutants.

    Close to 100 wildfires were active over the western United States as of Aug. 24, according to the Incident Information System.

    The buildup of heat will also increase the risk of wildfire ignition. The large fires can generate their own wind and add to firefighting difficulties.

    For the remainder of August, above-average temperatures are likely to continue over the western U.S.

    Static US Late August

    The jet stream will be displaced well to the north into western and central Canada through the end of August. The jet stream is a high-speed river of air where jets cruise at. South of this river, warmth is common.

    Normal temperatures trend downward a bit during late August. Temperatures during this period are likely to run 3 to 8 degrees above average.

    For example, the average high in Las Vegas is about 100 near the end of August. Highs may be within a few degrees of 105 in the city. Temperatures may approach 110 on occasion in Phoenix. The average high in Phoenix is about 105.

    The pattern may bring some days with highs near 80 in San Francisco. The average high is in the lower 70s.

    Thunderstorms may be few and far between from Idaho, Nevada and western Arizona on west from this weekend into next week. Spotty storms are likely to continue farther to the east in the region.

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