Extreme heat is about to expand in the West and broil many interior locations, due to a shift in the jet stream pattern during late June.
The jet stream is a river of fast-moving air high in the atmosphere that acts as a path for storm systems and separates cool air to its north from hot air to its south.
According to AccuWeather Chief Long Range Meteorologist Paul Pastelok, the jet stream will bulge northward in the West and sink southward in the East later next week.
"The West has already experienced some hot weather with the current jet stream pattern, but it will get even hotter during the last week or so of June and will remain very hot into early July," Pastelok said.
Thermal, Calif., was the hottest location in the world on Thursday, June 18, with temperatures reaching 119 degrees Fahrenheit. The Middle East usually has the highest official temperatures on a daily basis. Thermal set a new record high for the date on Thursday, but not a June record, which is 122 F set in 1994 and tied in 2013.
The extreme heat, even by summer standards, in the West will bring dangers to those partaking in strenuous physical activity.
The long-term heat and associated dryness will create difficulties for firefighting efforts and raise the risk of new wildfires breaking out.
More than two dozen wildfires were active during the middle of June in Washington, Oregon, Arizona, New Mexico and California, according to InciWeb. The currently active fires have consumed approximately 32,000 acres as of June 19.
As the jet stream bulges northward later next week, so will the hot air.
"Parts of the Northwest will likely have the greatest temperature departures from average as the pattern peaks near the end of June," Pastelok said.
Areas along the Pacific coast, such as Seattle, will experience temperatures around 20 degrees Fahrenheit above normal. In Spokane and other interior locations, temperature departures can reach 30 degrees Fahrenheit above average.
By next weekend, temperatures in Pendleton and Portland, Oregon; Spokane and The Dalles, Washington; Boise and Pocatello, Idaho; Reno, Nevada; and Salt Lake City may reach or exceed 100 F.
This is the type of pattern that will spare coastal California, such as San Francisco, Los Angeles and San Diego from the heat.
"The desert Southwest big cities, such as Las Vegas and Phoenix, will hit 110 F or higher, while Denver is looking at five days in a row with highs of 90 F or higher," Pastelok said.
The forecast 90-degree-Fahrenheit heat in Denver will be its longest streak so far this year.
While extreme heat usually visits much of the West during the summer, the heat wave forecast will be several weeks and, in some cases, a couple of months early.
"There is little hope for drenching rain through early July, but spotty storms could develop prior to the end of June in Southern California to the central Sierra Nevada as a disturbance may attempt to drift in from the Pacific Ocean," Pastelok said.
Another system forecast to move in from the Pacific during the first few days of July should scale back the heat in the Northwest.
"The system during early July could produce thunderstorms in Idaho, Montana and Wyoming, but how much rainfall occurs and how extensive the storms are in Washington and Oregon are questionable this far out," Pastelok said.