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    Late-week heat to challenge long-standing records, fuel wildfires across western US

    By Renee Duff, AccuWeather meteorologist
    July 06, 2017, 10:42:07 AM EDT

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    Extreme heat will build across the interior western United States and place long-standing records in jeopardy later this week.

    Multiple temperature records dating back to the mid- to late 1900s could be tied or broken during the peak of the heat late this week. A few of the records in jeopardy have stood since the early 1900s.

    The latest surge of hot air will be the most expansive heat wave so far this summer, with scorching conditions anticipated as far north as southern British Columbia and Alberta, Canada. On Friday, Calgary, Alberta, may come up just a few degrees shy of breaking the daily record high of 93 degrees Fahrenheit set in 1896.

    “High temperatures will be up to 15 degrees above normal for much of the week and upcoming weekend,” AccuWeather Meteorologist Brett Rathbun said.

    The heat will come in response to a large dome of high pressure building over the region, according to Rathbun. High pressure areas are mainly dry weather systems that can be attributed to intense heat waves during the warmer seasons.

    NW heat 7.5 AM

    By Thursday and Friday, daytime temperatures in the middle and upper 90s F will be common from the Great Basin through the northern Rockies and into southwestern Canada. Temperatures could exceed 20 degrees above normal in these areas.

    The 100-degree mark will be exceeded for multiple days in Salt Lake City and Boise, Idaho. Spokane, Washington, and Missoula, Montana, will come close to hitting the century mark. On Saturday, the temperature at Missoula could challenge a record of 101 set in 1918.

    The worst of the heat will stay east of Seattle and Portland, Oregon, though these cities experienced daytime temperatures in the middle 80s and lower 90s, respectively, on Wednesday. Similar conditions can be expected again on Thursday.

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    In the Southwest, the heat will not reach the extreme levels that were felt several weeks ago. Still, highs 5 to 10 degrees Fahrenheit above average could challenge records in Phoenix, Las Vegas and Palm Springs, California, by the end of the week.

    Those venturing on hiking trips across the West should drink plenty of water, wear lightweight attire and take frequent breaks in the shade to avoid heat-related illnesses or worse. Residents wanting to take pets on a walk should do so during the early morning hours when the pavement is much cooler. Check on elderly neighbors and those without air conditioning, and never leave pets or children inside a closed vehicle.

    Vegetation will continue to dry out under the scorching sun, providing a breeding ground for ongoing wildfires to spread and new wildfires to quickly ignite.

    Static Fire Weather

    Nearly three dozen large wildfires are raging across the West, according to the National Interagency Fire Center. This is up from about two dozen last week.

    The largest active blaze is the Brian Head Fire in southwestern Utah, which has burned over 68,000 acres. Fire crews have made significant progress on containing the fire since last week with 75 percent of the blaze now under control.

    “This heat will assist in ramping up the monsoon rain season across the Intermountain West,” Rathbun said.

    The increase in showers and thunderstorms can help douse ongoing blazes and temporarily moisten the dry ground.

    “However, the hot temperatures combined with any dry lightning strikes can ignite wildfires,” Rathbun said.

    This year's monsoon seems to be on schedule. On average, the increase in clouds and thunderstorms associated with the Southwest monsoon occurs during the first week of July.

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