A slow motion disaster will continue playing out in the western United States this weekend as the same weather pattern that kept the west dangerously hot and dry this past winter is back to roast it over an open fire beginning this weekend. Some locations will see highs in the 100s through the middle of next week.
The worst of the heat will go down in the valleys of the Intermountain West, with cities like Boise, Spokane, and Salt Lake City getting ready to see several days with high temperatures at and often well above 100°F during the worst of it. Here’s a signature Terrible Graphic From The Vane showing forecast highs from the National Weather Service over the next six days:
The highs in Boise and Spokane on Saturday and Sunday, as well as the highs in Kennewick on Friday, Saturday, and Sunday, all break daily high temperature records at each of the city’s airports. Records go back to 1940 in Boise, 1945 in Kennewick, and 1881 (!) in Spokane.
Some good news is that this will be a relatively dry heat. Dew points outside of desert areas will hover in the 40s and 50s for the duration of the heat wave. It’s not going to be skin-cracking dry, but the humidity isn’t going to be too much of an issue. Lower dew points makes the heat more tolerable—sweat evaporates from your skin more efficiently, allowing you to cool down easier than you would on an equally hot but muggy day in Orlando. The heat will be dangerous if you’re outside for too long without shade or plenty of water, sure, but it’s not going to be that stifling, choking heat you’d experience in the southeast.
While lower moisture is comfortable to us humans, it’s not always good news for our surroundings. Heat waves bring about the risk for wildfires, especially since much of the west is mired in such a deep drought. These elevated dew points will hopefully—hopefully—help stave off any widespread fire issues.
Low humidity, high heat, gusty winds, and parched land can set the stage for nasty wildfires, which has been something that we’ve been warning residents would happen for months, now. Numerous fires are already burning across the western United States and Canada, and the heat wave won’t help conditions.
The Storm Prediction Center—which also issues fire weather outlooks—doesn’t expect sufficiently low humidity levels to coincide with gusty winds in this region through the beginning of next week, which means that fire weather conditions aren’t favorable for the land to combust like the head of a match. Some fires are still possible, especially in areas that see thunderstorms, so if you live in a vulnerable area, keep an eye out in case you have to get out of Dodge in a hurry.
We’re still witnessing a slow motion disaster in that hot, mostly calm weather prevents the region from seeing any meaningful precipitation, which will only serve to worsen the drought and lead to the potential for more explosive wildfires as we head deeper into the summer.
Our upcoming pattern is a throwback to last winter, where we had a stubborn jet stream that produced an enormous ridge over the western half of North America while keeping the eastern half of the continent under the influence of a series of troughs. This pattern was responsible for both the West Coast staying extremely warm and dry for the duration of the season, while areas east of the Rockies saw one blast of bitterly cold weather after another, followed by the occasional foot or two of snow (or just a li’l bit more in Boston’s case).
The seed that will sprout the heat wave is already in place over the Pacific Northwest, and it will grow into a monster ridge/trough pattern over North America that looks like something you’d see in a meteorology textbook. Here’s a snapshot of the ridge/trough at the 500 millibar level (about 18,000 feet, give or take a few thousand) for this Sunday, according to the GFS model.
That large ridge over the western half of the continent isn’t the only player in the game. A trough in the east will allow the heat wave that’s baked the southeastern United States for the past two weeks to finally break. Today likely marks the end of the 12-day streak where the high temperature hit 97°F or warmer in Florence, South Carolina, falling three days shy of the city’s all-time excessive heat streak of 15 days set back in July 1993. Temperatures will cool off considerably the farther north you go—highs in the 60s in the Northeast sound good—but it mostly marks a return to seasonable ick rather than any sort of meaningful relief.
This pattern will likely stick around through the beginning of July, keeping the west abnormally warm and the east at or just slightly below normal (normal still being hot, of course).