The first full day of fall is here and it is wet. A large area of low pressure offshore with a ton of moisture in it has pushed the leading edge of rain over the area.
As the moisture slams into the Olympic and Cascade mountain ranges from the southwest, the mountains will force the moisture to rise, where the water vapor will condense into clouds and cause heavy rainfall. Also along with this “fire hose” of moisture from the Pacific, some gusty winds.
A Wind Advisory is in effect for the coast where winds could top 45mph in highest gusts. North/west of Everett through the San Juans, winds could gust in the 35-45 mph range. Around the rest of the lowlands, we could see gusts 25-35 mph. That doesn’t sound like much, but the first storm of the season usually produces unusually high number of power outages and tree damage.
In the mountains, two to four inches of rain is expected with even more possibly falling into Thursday and Friday, depending on the exact trajectory of the atmospheric river. This will cause rivers to rise, though I doubt we see any river flooding because all our rivers are low at the end of summer, especially so this September as it has been quite dry. The only exception: The Skokomish River in Mason County could approach flood stage during this event.
In the lowlands around Western Washington, including Puget Sound, we can expect a half-inch to more than an inch of rain through Wednesday night with even more rain falling in showers through Friday for a multi-day total of 2-3 inches, on average. Storm drains and gutters will overflow with debris from the summer, so urban flooding is a concern. I also expect a chance for thunderstorms today, especially once the cold front passes late tonight and into tonight.
For Thursday, we could have a few afternoon and evening thunderstorms with Friday bringing more rain with breezes.
We should see the wet weather settling down next weekend with some periods of sunshine but still some showers around, particularly Saturday.
Temperatures rebound next week with more sunshine so it’ll feel a bit like summer with highs back in the 70s.
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