Scorching Heat This Week in Pac NW; All-Time Hottest Month in Miami, Salt Lake City

July 30, 2017, 11:35 PM EDT

 
Above: In this Sunday, July 23, 2017, photo, the Lodgepole Complex fire burns near Sand Springs in eastern Montana. The massive fire destroyed at least a dozen homes and led ranchers to cut escape routes in fences for cattle. Image credit: Rebecca Noble/The Billings Gazette via AP.

One of the hottest weeks in decades is on tap for the Pacific Northwest. Excessive heat watches and warnings are in place from northern California to southern Washington. The intense heat will team up with gusty winds and a parched landscape to exacerbate the wildfire threat, especially later in the week, as dry thunderstorms may begin to enter the picture.

A stubborn, sprawling upper-level high will intensify during the week, favoring sinking air and sunny skies. This will be a multi-day ordeal for the region, with little relief until at least the weekend. Some all-time record highs could be in jeopardy across the Pacific Northwest, especially in the valleys just inland from the coastal mountain ranges. Here are some of the most vulnerable all-time records, together with WU forecasts issued on Sunday night:

Olympia, WA
All-time high: 104°F, most recently on July 29, 2009 (records begin in 1948)
Forecast high for Thursday:  106°F

Portland, OR
All-time high: 107°F, most recently on August 10, 1981 (records begin in 1940)
Forecast high for Thursday:  107°F

Eugene, OR
All-time high: 109°F on August 9, 1981 (records begin in 1912)
Forecast high for Wednesday:  110°F

Medford, OR
All-time high: 115°F on July 20, 1946 (records begin in 1911)
Forecast high for Wednesday:  114°F

Redding, CA
All-time high: 118°F on July 20, 1988 (records begin in 1983)
Forecast high for Wednesday: 115°F

Outlook for dry thunderstorms issued 7/30/2017, valid 8/6/2017
Figure 1. The extended fire-weather outlook from NOAA/SPC issued on Sunday afternoon highlighted the risk of dry thunderstorms for next Saturday and Sunday in the Pacific Northwest. Dry thunderstorms may also be on the increase in parts of California this week, according to Daniel Swain (California Weather Blog).

Heat waves like this are a recurrent feature of Pacific Northwest climate, but seldom are they this intense and prolonged. Eugene’s longest stretch of 100°F days is 4, most recently on July 29-August 1, 2015. The WU forecast of 100°F readings from Tuesday to Friday would match this record. Many buildings in the region lack air conditioning, so there is a real risk of heat-related illness as the heat stretches through multiple warm nights and sizzling days.

Wildfire risk on the rise this week across Northwest

Numerous fires have pockmarked the U.S. Northwest and southwest Canada over the last several weeks. With 270,000 acres burned as of Saturday, Montana’s Lodgepole Complex was the state’s largest fire since the disastrous fires of 1910, according to the National Interagency Fire Center (NIFC).

Unfortunately, the forecast doesn’t exactly offer good news for the Northwest. This week’s intense heat and dryness will dry out the landscape even further. The biggest threat may come over the weekend, as jet-stream impulses begin to tamp down the upper-level ridge. These impulses could help produce gusty southwest winds and scattered dry thunderstorms that would generate lightning but only scant amounts of rain.

Through July 30, the nation has seen a total of 5,279,544 acres consumed by wildfire, according to the NIFC. It’s the second largest year-to-date total of the last decade, topped only by the 6,052,366 acres burned by this date in 2010.

Ranch consumed by Lodgepole Complex fire in Montana, 7/25/2017
Figure 2. Tim Weyer tours his ranch, which was consumed by the Lodgepole fire complex, Tuesday, July 25, 2017 in Sand Springs, Montana. Image credit: Rion Sanders/The Great Falls Tribune via AP.

Salt Lake City and Miami: Hottest month in history

There’s never been a month as hot as this July has been in two widely dispersed U.S. cities: Miami, FL, and Salt Lake City, UT. Even though the month doesn’t officially end until midnight Monday night, it became clear days ago that July was on track to demolish the previous all-time monthly records in both cities. Records begin in 1874 in Salt Lake City and 1895 in Miami.

As of Saturday, July 29, the monthly average in Salt Lake City was 85.4°F. That’s more than a degree above the previous record for any month of 84.1°F (July 2013). The monthly average could drop by 0.1°F or 0.2°F once Sunday and Monday are factored in, but we can consider the record safely shattered.

In Miami, the average temperature through Saturday was 85.9°F, compared to the previous record for any month of 85.5°F (June 2010). The final reading is likely to drop by no more than 0.1°F. National Hurricane Center forecaster Eric Blake (@EricBlake12) pointed out the sheer insufferability of the past month’s heat in Miami: “This July has had as many days with a low > 80°F as the last 5 Julys combined!”

We'll have an update on Monday on the tropics, including Invest 98L, a non-tropical low that may undergo some development through Monday as it moves across the northeast Gulf of Mexico toward Florida.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Bob Henson

WU meteorologist Bob Henson, co-editor of Category 6, is the author of "Meteorology Today" and "The Thinking Person's Guide to Climate Change." Before joining WU, he was a longtime writer and editor at the University Corporation for Atmospheric Research in Boulder, CO.

bob.henson@weather.com

@bhensonweather

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