Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 150333 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 833 PM PDT Thu Jun 14 2018 .SYNOPSIS...
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After some clearing tonight, a weak upper level low will move south through the area Friday night. The low will stall over Oregon through about Monday, giving a chance of showers or thunderstorms in the Cascades each day. Temperatures will rise beginning Sunday, with highs in the 80s, possibly near 90 mid week.
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&& .SHORT TERM...
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A large upper trough remains centered east of the Cascades, but a small shortwave dropped over Western Washington today in the northwest flow aloft. The lower portion of the air mass remains fairly moist in low level onshore flow, with slight instability. The cumulus field that covered the area is gradually dissipating this evening, and the spotty light showers in the mountains are tapering off. Marine stratus should along the coast and spread part way inland tonight, and lows should be around 50. The flow will veer closer to northerly Friday and Friday night, with a weak shortwave dropping south across Western Washington or its coastal waters. This feature could produce some mountain showers and possibly isolated thunderstorms near the Cascades crest. For the lowlands, though, the marine stratus over the area in the morning should give way to some afternoon sunshine with highs in the 60s to lower 70s. The upper low will be over Oregon on Saturday, with northeast flow aloft across our forecast area. Aside from a few showers over the Cascades -- and possibly afternoon/evening thunderstorms near the crest -- it will be a mostly sunny and warmer day, with highs in the 70s. The upper low will drift a bit further south on Sunday, with northeast flow aloft continuing over Western Washington. Again, isolated convection is possible over the Cascades, but otherwise it will be sunny and warmer yet; highs will be in the 70s at the coast and in the upper 70s and 80s inland. McDonnal .LONG TERM...Here is the long term section from the afternoon forecast discussion -- The upper low, now with less punch but still able to spawn the occasional shower, will probably remain relatively close Tuesday through Thursday. The GFS and Euro are in broad agreement, moving the low into Idaho Tuesday and Wednesday, then moving it a bit closer on Thursday. Have kept a dry forecast for Tuesday and Wednesday, and introduced showers in the Cascades Thursday. Highs will be in the 80s over inland areas all three days, with low 90s possible. Cooling is possible Thursday, especially on the coast where onshore flow could lower temps into the 60s. Burke
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&& .AVIATION...
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A broad upper trough will be over the area tonight and Friday with light northwest flow aloft. At the surface, light onshore flow will continue. The air mass is moist and slightly unstable. Ceilings will be generally 5000-8000 ft through this evening. MVFR low clouds will develop across a good portion of the area late tonight and Friday morning. The low clouds will lift and scatter on Friday with 5000-8000 foot ceilings again in the afternoon. KSEA...Ceilings 5000-8000 feet through most of tonight. MVFR low clouds should redevelop Friday morning. Westerly wind 4-8 knots will become northerly this evening. Schneider/McDonnal
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&& .MARINE...
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Onshore flow will continue for the next several days with high pressure offshore and lower pressure east of the Cascades. The onshore flow is expected to weaken slightly and turn a bit more northwesterly this weekend. Small craft advisory strength west winds are likely in the Central and Eastern Strait of Juan de Fuca most evenings into the first half of next week. Small craft advisory strength northwest winds are also expected at times for the Coastal Waters Friday through Sunday. Schneider/McDonnal
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&& .SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None. PZ...Small Craft Advisory from 2 PM Friday to midnight PDT Friday night for Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Small Craft Advisory from noon Friday to 6 AM PDT Saturday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. Small Craft Advisory until 3 AM PDT Friday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.
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&& $$ www.weather.gov/seattle

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