Record heat to scorch the West into the first half of the upcoming week
The largely cooler-than-average weather pattern of late is currently in the process of flipping very quickly, and we’ll be talking about record heat in many areas of the West from Sunday through Wednesday.
The trough scooting across the West early in the weekend will lift out by Sunday, and a ridge will start to build in its place. As it does so, the heat will begin to build.
The heat will be felt first in southwestern Oregon and the San Francisco Bay Area on Sunday, where temperatures will surge well into the 80s to near 90 under a lot of sunshine. Just inland from the Bay, temperatures will surge even higher - reaching up to near 100 degrees Fahrenheit in places like San Jose and Pleasanton.
Heading into early next week, the area impacted by the heat will grow. It will expand across the Pacific Northwest and through the Central Valley of California, and then continue to slide eastward toward the Rockies.
Temperatures in most places will be 5 to 15 degrees above average, but in some extreme cases could reach 20 to 25 degrees below average. Places like San Francisco, Medford and Portland will be the most likely to have the most extreme departures from average.
By Tuesday and Wednesday, a fairly weak trough will be sitting off the West coast. This trough will help to pump the ridge even more in the short-term in the Pacific Northwest, and will allow temperatures to reach record levels as the offshore flow continues.
An upper-level forecast valid late Tuesday, showing the ridge in the West and the weak trough that will ultimately end the heat later in the week.
Portland could surpass 95 degrees by Wednesday, and the records on both Tuesday and Wednesday will be in jeopardy. Seattle could flirt with records by Wednesday, with temperatures getting well into the 80s. Given how warm the air mass is aloft, it’s not out of the question that the Emerald City gets close to 90 on Wednesday.
One area that will not really be impacted by this heat wave is coastal Southern California. Temperatures will rise above average, but it won’t be record heat by any stretch. Downtown Los Angeles will reach the 80s and San Diego will have temperatures rise well into the 70s.
The GFS model (from the early Saturday morning run) showing forecast high temperatures near the surface on Wednesday. Don't necessarily focus on the specific numbers here, but this image illustrates just how significant and widespread the heat will be during the early part of the week.
The orientation of the ridge and the approaching trough will keep an onshore flow near the surface in coastal areas. While the marine layer will not spread as far inland as many recent days, it should still hang near the coast with the onshore flow.
Inland areas will reach the 80s and 90s, but it’s certainly not as hot as these areas can get this time of year. To get into the really hot stuff across SoCal, you’ll have to venture into the high deserts, and temperatures will likely top 110 degrees in the Coachella Valley.
While we’re talking about 110 degrees, Phoenix may reach that level by Tuesday or Wednesday. After some very cool stretches in May, this would be a pretty typical point in the year to reach 110. The first 110-degree day of each of the past three years were June 4th, June 17th and June 3rd, so this year will fall right in that range.
The ridge will flatten late next week into the weekend, which will send temperatures closer to average levels. This will likely persist into the third week of June, so this looks to be the last widespread heat wave in the West for a little while.
With this hot, dry weather moving in, the wildfire danger has increased. It has spiked this weekend in the Sacramento Valley where Red Flag Warnings have been up thanks to the combination of gusty winds and low humidity.
While the wind will subside some in the coming days and humidity levels will rise slightly, the hot and dry conditions will continue to pose a wildfire threat. The diminishing wind, though, will reduce the threat for rapidly spreading fires in most places.
As long as the ridge is in control, there will be virtually no rain across the West in the coming days. As the trough slides in and the ridge flattens later next week, we’ll likely start to see some high-elevation thunderstorms popping up again.
One other thing to note is the appearance of "severe drought" on this past Thursday's Drought Monitor across the Olympic Peninsula.
A look at Washington State in the latest U.S. Drought Monitor. The darker brown area in westernmost Washington is the area now listed as in "severe drought." (Image/Drought Monitor)
While the most recent trough did bring some welcome rain to parts of this area (about 0.6 of an inch in Quillayute and 0.11 of an inch in Seattle), it really wasn't enough to make much of a dent in the rainfall deficits in this area.
Looking down the pike, it could be another 10-14 days before any rain chances return. As we head into the dry seasons, opportunities to alleviate this drought will be few and far between.
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