A unfortunately hot week is in store for the western US thanks to a large and expanding ridge of high pressure, allowing for most dry weather conditions and well above-average temperatures. These conditions will just make the environment more conducive for wildfires, many of which have already burned thousands of acres. Currently located over the southwestern US, this ridge will expand to the north, becoming dominant across the western half of the nation by the end of this week.
This Tuesday, the worst of the heat will be in the Southwest, with numerous daily record highs expected to be broken as temperatures surge into the 100s. Even the immediate coast will be hot, with highs in the 80s and 90s, about 15 degrees above-average. Los Angeles is forecast to get up to 97 degrees, and in Death Valley temperatures may reach 125 degrees. For reference, their hottest day so far this year featured a high temperature of 127 degrees.
Up the coast, high temperatures into the 90s and 100s will be very common for the metro areas, and even parts of the valleys in eastern Washington may soar into the 100s this afternoon, which pretty uncommon for those areas. Seattle has experienced 23 days of temperatures of at least 85 degrees so far this year, breaking the previous record of 22 days from 2015. That tally should continue Tuesday through Thursday, before a cool down moves into the Pacific Northwest by the weekend.
On Wednesday, the ridge will begin to work northward across the interior West, centering over Nevada. This will allow for the 100-plus degree temperatures to become even more prevalent. Once again, highs into the 90s and 100s will be common across most of the West on Wednesday, with the exception of the higher elevations. In Los Angeles, there have been 3 90-plus degree days so far this year, which is the 9th most year-to-date. The city is forecast to experience highs in the 90s Tuesday through at least Friday, which will bring it over the record of 6.
While temperatures cool off by just a degree or two by Thursday in the Southwest, the Northwest will experience a peak in temperatures, with widespread highs into the 90s and 100s. A few localized locations may top off near 110 degrees, which is definitely record-breaking. A state like Montana will see temperatures into the 100s by the afternoon.
By Friday, an onshore flow will significantly cool down the Pacific Northwest, bringing temperatures down to the 70s. Just east of the Cascade Mountains, temperatures will remain in the 90s and 100s, nearly 30 degrees above-average. Much of the Southwest will remain hot, following a similar temperatures profile as Wednesday and Thursday, though the southern half of Arizona and New Mexico will deal with temperatures around of 10 degrees below-average.
This cooler air will invade into more of the Northwest on Saturday, before temperatures turn back to above-average across most of the West by the end of this upcoming weekend. Thankfully, this second round of heat will not be an intense.