Western Heat Wave Intensifies Friday; May Break June, All-Time Records This Weekend Into Early July (FORECAST)

Jon Erdman
Published: June 25,2015

A brutal heat wave is about to shift into high gear and may shatter June or even a few all-time records in parts of the Great Basin and Northwest. Furthermore, it may last into the first days of July.
The National Weather Service has issued an excessive heat warning for parts of northwest Oregon and southwest Washington, including Portland, Salem, Eugene and Vancouver. An excessive heat watch is posted farther north in western Washington, including Seattle and Tacoma. Heat advisories have also been posted for other parts of the Northwest.

Heat Alerts

June has already been a hot month in parts of the West.
Earlier in the month, Yakima, Washington, tied its all-time June high of 105 degrees. This occurred 15 days earlier on the calendar than the previous June 105-degree high. Medford, Oregon, is pacing for their hottest June on record, dating to 1911. Portland, Oregon, has already tallied 5 days of 90-degree-plus heat this month through Thursday, just one day shy of the June record set in 2003.
(MORE: All-time Record June Heat in the Northwest | Earth's Record Warmest Year?)
The culprit in this hot setup is part of an overall pattern shift taking place this week across the United States.

West Heat Wave Setup

A dome of high pressure aloft that has been searing the Desert Southwest over the past week will surge northwestward, becoming established over the Great Basin by this weekend.
In addition to suppressing thunderstorm development over much of the Great Basin, this will allow the sizzling late-June sun to send temperatures soaring not simply in the typically hot Desert Southwest, but also locations well to the north including the Pacific Northwest, interior Northwest and northern Rockies.
By Friday into the weekend, highs in the triple digits are expected in many lower-elevation locations west of the Continental Divide and inland from the Pacific Coast.
This includes parts of Nevada, California's Central Valley, the Salt Lake Valley, Idaho's Snake River Plain, much of Oregon's lower elevations east of the immediate coast, and areas to the east of the Cascades in Washington State. Valley locations in western Montana such as Kalispell and Missoula will also top the century mark by this weekend into early next week.
In particular, parts of the Columbia Basin and lower Snake River Valley may surge above 110 degrees. This includes cities such as Yakima, Kennewick and Walla Walla in Washington as well as Lewiston, Idaho.
(FORECASTS: Seattle | Portland | Boise | Salt Lake City)

Forecast Highs

The extreme heat is even expected to surge north into Canada. Even Revelstoke, British Columbia – 130 miles north of the U.S. border and better known for skiing – could touch 100 degrees (38 degrees Celsius) this weekend.
Compared to what the more arid Great Basin is used to, evening and overnight temperatures will be slow to drop, bottoming out in the 70s in the hottest locations.
This heat appears to be locked in place well into next week, as the upper-level dome of high pressure remains camped out near the Great Basin.
(MAPS: 10-Day Temperature Forecasts)
The hot, dry weather will also produce high fire danger, as drought conditions have worsened over the Northwest and northern Rockies in the spring. Disturbances riding around the west side of the upper-level ridge and just enough mid-level moisture may trigger isolated, mainly dry afternoon thunderstorms, which may ignite new wildfires.
(MORE: Western Wildfires Latest News)
In mid-May, Washington Gov. Jay Inslee issued a statewide drought emergency, and spring runoff from winter's paltry snowpack was expected to be the least in 64 years.
Seattle has seen only 7 days with measurable rain since May 1, one-third the average number of such days, according to NWS-Seattle. Portland, Oregon, set a new record June dry streak of 21 straight days through Wednesday, according to NWS-Portland.

Gerard Tangalan Of Seattle leans on International Fountain while cooling off at the Seattle Center July 29, 2009 in Seattle, Washington.
(Stephen Brashear/Getty Images)

Monthly, All-Time Records Threatened?

This heat wave may not only top daily record highs, but may also threaten record highs for the entire month of June, or, in a few locations, all-time record highs.
Here are some locations that may flirt with – we're defining that as within 3 degrees – either their June or all-time record highs. Click on the city link for the latest 10-day forecast.

• Yakima, Washington: All-time record is 111 degrees on July 26, 1928
• Spokane, Washington: All-time record is 108 degrees on July 26, 1928 and Aug. 4, 1961
• Boise, Idaho: All-time record is 111 degrees on July 19, 1960 and July 12, 1898
• Salt Lake City: June record is 105 degrees on June 28-29, 2013
• Kennewick, Washington: June record high is 110 degrees on June 7, 1912
• Portland, Oregon: June record high is 102 degrees on June 26, 2006
• Pendleton, Oregon: June record high is 108 degrees on June 30, 1924, and June 17, 1961
• Reno, Nevada: June record is 104 degrees on June 16, 1940
• Kalispell, Montana: All-time record high is 105 degrees on Aug. 4, 1961. 
• Missoula, Montana: June record high is 100 degrees on Jun. 29, 1937 and Jun. 13, 1918. 

One of the biggest factors in heat wave deaths is not only the magnitude, but also the longevity of the heat.

• Seattle may see highs reach at least the low 90s for several days, starting this weekend. On average, they typically see the 90-degree mark only three days a year.
• Spokane, Washington may see a couple of days with century-mark highs. Only one such day a year is the average, there. Even when not in the 100s it will be at least in the middle or uppper 90s.
• Portland, Oregon last saw triple-digit heat in August 2012. They may see at least one, if not more in this heat wave. The city may also make a run at its longest streak of 90-degree days; that was a 10-day streak in 2009.
• Pendleton, Oregon may threaten its all-time record of eight consecutive 100-degree days set in five previous years, most recently in 1967.
• Salt Lake City may see triple-digit highs several days in a row from the weekend into next week. Six days a year reach 100-degrees or hotter in the Salt Lake Valley, on average.
• Kalispell, Montana may see two or three days in a row of triple-digit heat beginning this weekend. In records dating to 1899, they've only seen 12 such days, only two of which have occurred this century. They have never recorded a triple-digit high in June.

This is a dangerous heat wave. Take safety precautions against the heat.
Those playing or working outdoors, as well as those without access to air conditioning, will face an elevated risk of heat-related illness.
Remember to never leave kids or pets unattended in cars and drink more water than usual. Wear light-colored clothing and keep your head and body cooler with a hat. Take frequent rest breaks in shaded or air-conditioned environments.
Senior meteorologist Nick Wiltgen contributed to this report.

MORE: Heat Waves of the Past (PHOTOS)