We are finally starting to see some summer-like weather over the Pacific Northwest. I went for a nice bike ride on Sunday down to West Point in Discovery Park, and the weather was absolutely perfect, with highs touching 70 degrees at Sea-Tac and a mix of clouds and sun. Tons of riders were out on the Burke-Gilman trail, and many people were walking on the beach and hiking around Discovery Park. I even heard some UW students playing their trumpets as I rode by the Montlake cut, serenading the boaters as they motored by.
Alas, rain will return to the Pacific Northwest Thursday evening and will persist through Memorial Day weekend. And portions of SW Washington, most of Oregon, and much of the Intermountain West should see particularly heavy rain this weekend, with another, late-season bout of snow in the mountains. Let’s take a look.
Current Conditions
The Western US is currently under the influence of a large ridge of high pressure centered over California. The Central Valley is expected to see record highs today with temperatures rising into the triple digits over much of the area, while the Great Basin and Desert SW are expected to see some of their warmest temperatures of the year but not quite reach record territory.
However, much of coastal California – especially Southern California, is only expected to see near-average temperatures. This is due to onshore flow at the surface bringing cool, marine air to coastal cities. The weather balloon sounding from Santa Barbara this morning shows this well – note the massive inversion in the lowest levels of the atmosphere. Temps were 50 at the surface, but 80 degrees just 500 meters above!
Credit: Storm Prediction Center
Satellite imagery also shows this well, with low clouds along the California Coast spreading northward while bluebird skies can be found over the Central Valley. The ridge is much weaker over the Pacific Northwest, which is seeing partly cloudy skies as high clouds ahead of an incoming system stream over the region.
100s in Central Valley today, but 60s for San Francisco, San Diego and other major California coastal cities.
Reason? Onshore flow brings cool air to the coast, while strong ridge brings record temps inland. Note the low coastal clouds in the satellite animation below. pic.twitter.com/S9M7UFDkCo
— Charlie Phillips (@WeatherPhillips) May 25, 2022
Thursday Evening – Monday: Cool and Wet
Those high clouds over the Pacific Northwest will thicken and lower tomorrow, and by tomorrow evening, rain should be falling over most of Western Washington and Northwest Oregon, with the heaviest precipitation over the Cascades and Coast Range/Olympics.
A few showers may persist Friday (mainly in the mountains) before an even stronger, cooler, and wetter system arrives on Saturday. This system will be aimed towards Oregon and, in some ways, resembles the system that brought the very rare, late-season lowland snowstorm on April 11, albeit much weaker and warmer than the April system.
Precipitation totals from Saturday’s system alone could reach 0.5 – 1.5 inches from SW Washington through the Southern Willamette Valley, and could be as high as 1-3 inches in the Oregon Cascades due to favorable orographic (terrain-induced) enhancement, as this system will be approaching directly from the west and winds should be perpendicular to the Cascades.
Credit: University of Washington
This system will also bring heavy rain/mountain snow to the inland Northwest and Rockies as it travels inland Sunday and early Monday. Nearly all of the Western US outside of Western Washington/Oregon is in some type of drought, and while this system won’t erase the drought by any stretch, it will still help significantly with some of the shorter-term fire and drought concerns as we head into summer.
Additionally, highs should only reach the mid 50s over Western Washington and Northwest Oregon on Saturday and Sunday, and several inches of snow should fall in the Cascades above 5000-6000 feet. The higher elevations of the Oregon Cascades and the Northern US Rockies could see up to a foot of snow from this system between Saturday evening and Monday evening – very impressive for Memorial Day weekend!
Credit: University of Washington
Next Week: Seasonably Warm and Mostly Sunny
Monday will be a “transition day” for the Pacific Northwest with near average temperatures and partly cloudy skies, but by Tuesday, a weak ridge of high pressure should return to the region and give us warmer and sunnier weather – probably a little warmer/sunnier than the weather we’ve seen this week, but nothing exceptional.
Unlike this week, I’m not expecting record temperatures for the Central Valley or the Desert SW, but temperatures should still be plenty warm there, with highs likely rising to the upper 80s-low 90s for Sacramento and the low-mid 100s for Phoenix. We will be in June by that time, after all.
To summarize:
- A strong ridge centered over California is currently bringing record heat to the Central Valley, while the Pacific Northwest and much of the California coast are experiencing more seasonable conditions due to weaker ridging/low-level onshore flow.
- A front will bring light rain to the Pacific Northwest tomorrow evening, with a few showers persisting Friday (mainly in the mountains)
- A much stronger system will take aim at Southern Washington and much of Oregon on Saturday and will progress inland Sunday and Monday. This system could bring 0.5 – 1.5 inches of rain from SW Washington through the Willamette Valley, with light snow in the Cascades above 5,000 feet and up to a foot of snow possible in the highest elevations of the Oregon Cascades and Northern Rockies. This will be great for decreasing early-season fire danger but may throw a wrench in some Memorial Day weekend plans, so plan accordingly!
- Sunshine and slightly warmer-than-average temperatures should return next week, along with higher streamflows as mountain snow over the Pacific Northwest continues to melt.
Enjoy the sun this week today and next week, and prepare for some unseasonably wet/cold weather this weekend!
Charlie
