Call it the zombie weather pattern: Just when you thought it was dead, it goes on. And on. And on.
As has occurred frequently over at least the past year, a massive dome of high pressure, known to meteorologists as a "ridge" in the upper atmosphere, is setting up across the West. This time, the high pressure area will act like a dome, trapping heat underneath and leading to dangerously hot and dry weather across the West.
Triple-digit heat is likely this weekend from Las Vegas to Portland, Oregon, with excessive heat warnings and heat advisories issued for millions. Along with the heat will come extraordinarily high fire danger, given the combination of long-term drought conditions, extreme heat and low humidity. In addition, winds will pick up in some areas around the periphery of the high pressure center, fanning any fires that ignite.
The heat may not be unusual for places like Vegas or Reno, but it poses a health threat in areas like Portland, Spokane, Eugene and Boise, all of which are forecast to see high temperatures eclipse 100 degrees Fahrenheit between Saturday and Wednesday. In Death Valley, California, which is typically the hottest place in the U.S., is likely to see temperatures climb into the low 120s Fahrenheit.
In addition, temperatures may rise into the lower 100s Fahrenheit in parts of California's Central Valley, near Salt Lake City, in parts of Idaho and eastern Oregon as well as western Montana.
The heat wave won't stop at the Canadian border, either, since the high pressure ridge will buckle the jet stream northward into British Columbia, forcing weather systems to detour around it. According to Environment Canada, parts of southern British Columbia may hit 40 degrees Celsius, or 104 degrees Fahrenheit. If this happens, it could break monthly temperature records in this area.
Drought has increased in WRN #Montana = Moderate Drought. Cntrl Id - severe drought. http://t.co/r7TorqegS0 #mtwx pic.twitter.com/ceuOUMGyHZ— NWS Missoula (@NWSMissoula) June 26, 2015
According to The Weather Channel, Kalispell, Montana, which is in the western part of the state, may see up to three days in a row of triple-digit heat starting during the weekend. This is in stark contrast to the historical record there, with only 12 triple-digit days occurring since 1899. Not a single 100-degree reading has occurred in Kalispell during the month of June, the network reported on its website.
In places like the Pacific Northwest, it is unusual to have a heat wave of this severity at this time of year, which is concerning since heat waves can be especially deadly when they strike early in the summer, before people are accustomed to warm weather.
The National Weather Service in Portland, for example, put out a statement warning area residents to "Be sure to avoid exertion during the heat of the day... and to stay hydrated with clear liquids." It also warned not to leave pets and children in cars, which can rapidly heat up and cause heat-related illnesses.
While the California drought has garnered the most media attention, there are also drought conditions in Oregon and Washington, with elevated fire danger there too. The Weather Service has issued an array of red flag warnings across the intermountain West and Pacific Northwest, which mean that conditions will be conducive to wildfire initiation and spreading.
Heat exhaustion and heat stroke can be dangerous. Know the warning signs & symptoms and how to react! #HeatSafety pic.twitter.com/5x4OTDqKUp— NWS Portland (@NWSPortland) June 26, 2015
Virtually 100% of Pacific NW abnormally dry or in #drought http://t.co/U0MnPaeQtA pic.twitter.com/PoDPBkqpxa— NIDIS (@DroughtGov) June 25, 2015
The heat wave may begin to abate by midweek next week. But the weather pattern responsible for it, which is characterized by a high pressure ridge in the West, and a trough, or dip in the jet stream, across the East, has been so resilient that it surely will be back again for potentially several more rounds this summer.
This weather pattern reinforces the drought by elevating temperatures and increasing evaporation, and it's helping lead to California's hottest year-to-date, following on the heels of its hottest year on record, which occurred in 2014.
True to form, some computer model projections show a brief break occurring late next week, followed by another round of a large western heat dome in early-to-mid July.