Good morning everybody!
In some ways, this summer and last summer are polar opposites. Last summer, we saw heat wave after heat wave throughout June and July, and this, coupled with a historically poor snowpack from the previous winter, led to water shortages throughout the region and extremely high fire danger throughout much of the Pacific Northwest. Then, August came, and with it came some much-needed rainfall and more moderate temperatures as Sea-Tac recorded its third-wettest August on record. On the other hand, we started out with near-normal rainfall and average or even below-average temperatures for June and July of this summer as a series of upper-level troughs continuously set up shop over our area, directing cool, moist Pacific air into our region, but since August, this trough has been usurped by a persistent ridge of high pressure in the Eastern Pacific that has since brought blue skies and warm temperatures to the area. Last Friday, we hit 90 degrees at Sea-Tac for the first time since June 5, but believe it or not, this week is going to be even warmer!
Credit: University of Washington Atmospheric Sciences Department
See the counterclockwise swirl of clouds off the coast, some 30 miles west of Destruction Island? That swirl marks the center of an extremely weak low pressure system that came through last night and has brought some marine stratus to the Strait of Juan de Fuca, coast, and southwest interior. As of 11 am though, Puget SoundElsewhere, it is sunny and clear. There was a bunch of advection fog around Puget Sound yesterday morning, making Seattle look more like San Francisco, but skies were as blue as could be around Elliot Bay this morning.
Credit: University of Washington Atmospheric Sciences Department
A strong upper-level ridge is currently centered over the northeast Pacific, and it will move east into our area as the rest of the week goes on. This, combined with offshore flow in the lowest levels of the atmosphere due to a thermal trough along the coast will help highs on Thursday, Friday, and Saturday approach and/or break record levels. Thursday/Friday will be the hottest for places on the coast, while Friday/Saturday will be hotter for places further inland along the I-5 corridor like Seattle. In Seattle, expect highs to approach 90 on Thursday, climbing into the low-mid 90s Friday and Saturday. This could likely be the hottest period we’ve had so far this year.
We currently have a “fire weather watch” and “excessive heat watch” over our area. But if you think that’s bad, be thankful you don’t live in the Willamette Valley! They have a red flag warning in effect, and highs there on Friday are expected to soar over 100 degrees in many locations, including downtown Portland. The Willamette Valley is commonly 5-10 degrees hotter than the Puget Sound Lowlands during these heat waves, as they do not have the benefit of local seabreezes from Puget Sound helping keep temperatures down.
Saturday, the thermal trough starts to move onshore, meaning the coast should transition to cooler onshore flow later in the afternoon. Nevertheless, they will still be quite hot earlier in the day, and onshore flow should reach the I-5 corridor well after maximum afternoon temperatures have already been reached. On Sunday, we cool off a couple degrees back into the upper 80s in Seattle, and by next week, onshore flow should return, bringing our temperatures back to more seasonable levels.
If you missed the opportunity to go swimming last week, here’s your chance!
Charlie