Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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252 FXUS66 KSEW 162219 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 319 PM PDT Sat Jun 16 2018 .SYNOPSIS...A weak upper level low will stall over southern Oregon and northern California tonight with a chance of showers or thunderstorms over the Cascades. High pressure will build offshore Sunday and Monday with ridge shifting inland Tuesday night and Wednesday. High temperatures will trend around 10 to 20 degrees warmer than normal. Increasing onshore flow will result in cooler temperatures over the interior on Thursday and Friday. && .SHORT TERM...An upper level low is spinning over southern Oregon this afternoon. Satellite shows some wrap-around moisture associated with the low and thunderstorms are popping up along the Cascades. Showers and thunderstorms will diminish this evening as the low exits. A strong upper level ridge will build offshore on Sunday then nudge inland early next week for a warming trend. Dry northerly flow will prevail Sunday and Monday with skies mostly clear. The warm air mass will lead to above normal temperatures with highs reaching the mid to upper 80s in the interior, around 10-20 degrees warmer than normal. Along the coast, surface pressure gradients remain onshore with a tight temperature gradient expected. Temperatures along the beaches will be in the 60s to lower 70s with 80s inland. Models are showing a marine push Monday night into Tuesday with stratus clouds possibly pushing into the interior. The stratus deck will be shallow and will burn back to the coast during the early afternoon. Models are showing a few showers developing over the Cascades where the air mass will be warm and unstable. Isolated thunderstorms are possible. 33 .LONG TERM...Wednesday will be the last day of the warm spell as the ridge moves overhead. Temperatures in the interior will peak in the mid to upper 80s with a few low 90s possible. Showers and isolated thunderstorms are possible in the mountains again, especially the Cascades. A strong onshore push will bring cooler conditions as we move into Thursday with highs mainly in the mid 60s to 70s. An upper level ridge will cross the Pac NW Friday and Saturday for more dry weather. 33 && .AVIATION...An upper level ridge offshore will continue expanding E over the area thru tonight while the upper level low over OR drifts S. This will result in nly flow aloft over wrn WA. Low level onshore flow will become offshore overnight. Meanwhile, the tstm threat over the Cascades will end this evening as the air mass stabilizes. There may be patchy IFR CIGs late tonight or Sunday morning. KSEA...VFR. Expect northerly winds thru Sunday afternoon. Wind speeds will be the strongest during the afternoon. Please see the TAF for specific details. && .MARINE...The flow will become light offshore or northerly tonight due to a 1020 mb high briefly setting up over British Columbia. Onshore or NW flow will return Sunday afternoon before becoming offshore Sunday night. Onshore or westerly flow will return Monday afternoon and then strengthen for the possibility of gale force winds over parts of the Strait of Juan de Fuca. Anticipate onshore flow of varying strength Tuesday through Thursday. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening 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 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 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 9 PM PDT this evening for Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.