Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 170237 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 737 PM PDT Mon May 16 2022 .SYNOPSIS...
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A few showers over Western Washington this evening will give way to a mostly dry day on Tuesday as weak high pressure shifts over the area. A vigorous frontal system will move through Western Washington on Wednesday for a period of wet, blustery weather. A cool upper level trough will be over the area Wednesday night and Thursday. High pressure should build over the region around the end of the week.
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&& .SHORT TERM /TONIGHT THROUGH THURSDAY/...
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There are a few showers over Western Washington this evening--mainly in the foothills of the central Cascades, along the coast, and in a narrow convergence zone over the Quimper Peninsula--otherwise, there were no updates to the forecast this evening. 19 A brief break in the unsettled weather is then in store on Tuesday as the upper level trough influencing the region weakens and flow aloft becomes more zonal. Ample low level moisture across the region will still render some cloud cover, however- but can expect to see some partly sunny skies across portions of the area. Highs on Tuesday will again be in the mid 50s to low 60s across the region. The next, more vigorous frontal system will then move across Western Washington on Wednesday. While guidance remains in decent agreement regarding the timing of the system, there still remain discrepancies on its strength. Latest GEFS ensemble members have been highlighting mean max wind gusts in the 25-35 mph range for much of the area, while latest ECMWF ensemble guidance continues to show gusts in the 35-45 mph range. Meanwhile, 4.1 NBM probabilistic guidance highlights a 55-60% chance of wind gusts exceeding 45 mph for portions of Whatcom County and the North Coast. At a minimum, it looks like it will be a pretty gusty day across the region- especially given the time of year. The windiest spots look to be areas across the North Coast and across the Northern Interior. Overall, have maintained the trend towards the stronger solutions for now with the afternoon forecast package. In addition to winds, another important aspect to the forecast will be the precipitation in the mountains- which will be susceptible to good orographic forcing. Current forecast has snow levels generally between 4000-4500 feet on Wednesday, dropping to around 3000 feet by Thursday morning. Latest forecast calls for 12-18 inches of new snow possible at Mount Baker by Thursday morning and 8-12 inches of snow near Paradise. Snow will be possible at the passes as well- with Stevens potentially getting anywhere from 4-6 inches by Thursday morning. Strong onshore flow behind the front will likely produce a convergence zone across the North-Central Sound, so locally higher amounts of snow will be possible for the mountains should any heavier bands develop. Those with plans to recreate in the mountains and to travel across the passes midweek will want to make sure to stay updated on the latest forecast and WSDOT pass conditions before heading out. A cool upper level trough will then swing across the region on Thursday, keeping showery weather in the forecast into the second half of the week. Afternoon high temperatures will be in the mid to upper 50s. 14 .LONG TERM /FRIDAY THROUGH MONDAY/...Weak upper level ridging will start to build in from the west early in the long term, giving Western Washington a dry break on Friday. Discrepancies remain amongst guidance regarding the timing of the next frontal system over the weekend. The GFS and its associated ensemble suite hold the precipitation off until Sunday for most of the area, while the ECMWF brings the precipitation into Western Washington Saturday afternoon and evening. Latest NBM guidance has kept chances of rain for the coast and Olympic Peninsula, so have maintained that in the forecast for now. Unsettled conditions then look to persist into early next week. 14
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&& .AVIATION...
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Onshore flow will ease overnight. It seems likely that areas of clouds will set up overnight and then burn off or dissipate in typical fashion on Tuesday. Mid and high clouds will increase Tuesday afternoon or evening as the next front approaches. 19 KSEA...The breeze seems to want to be westerly this evening but should become light and variable tonight and Tuesday before the next front arrives later Tuesday night. We might see lower clouds setting up overnight than is currently in the forecast with light onshore flow and a stabilizing air mass but for now I will only lower the cigs a notch for the morning hours. 19
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&& .MARINE...Onshore flow will ease as high pressure shifts over Western Washington through Tuesday. A vigorous frontal system will approach the area Tuesday night. The associated low pressure center will deepen to around 990mb and reach northern Vancouver Island by daybreak Wednesday. The front will move through Western Washington Wednesday morning with blustery winds and gales possible--mainly over the coastal waters. Onshore flow behind the front will ease Wednesday night and Thursday. 19 && .HYDROLOGY...The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated as needed until then. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Gale Watch from late Tuesday night through Wednesday afternoon for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Small Craft Advisory until 5 AM PDT Tuesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 11 PM PDT this evening for Northern Inland Waters Including The San Juan Islands. Small Craft Advisory until 5 PM PDT this afternoon for Puget Sound and Hood Canal. && $$ www.weather.gov/seattle

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