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Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
879 FXUS66 KSEW 111527 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 827 AM PDT Tue Jun 11 2024 .SYNOPSIS...Upper level trough moving through Western Washington today. Zonal flow aloft tonight into Wednesday with a weak ridge of high pressure building Wednesday night into Thursday. Cool upper level low moving southeast out of the Gulf of Alaska late in the week. System spinning out of the low moving through Friday with the low overhead for the weekend. The low will move southeast Monday. && .UPDATE...A weak frontal system is moving east across the region this morning producing some light rain showers. Minor updates were made to the forecast to account for the latest trends and short range forecasts. Impacts will be mainly limited to areas of wet roadways. The rest of the forecast is on track and no further updates are expected. -Wolcott- && .SHORT TERM /TODAY THROUGH THURSDAY/...Satellite imagery shows upper level trough with a weak cold front just offshore early this morning. Mostly cloudy skies west of Puget Sound. Partly cloudy skies east of Puget Sound. Temperatures at 3 am/10z were in the 50s. Upper level trough and the weak front moving through Western Washington this morning. Satellite imagery shows cloud top temperatures not cold at all with the front. A good indicator that there will be little in the way of precipitation with the system. Best chances for showers this morning over the northern portion of the area. It will get breezy near the Strait of Juan de Fuca later this morning into the afternoon hours with increasing low level onshore flow behind the front. Weak convergence zone developing over Snohomish county will keep skies more cloudy there than the rest of the area this afternoon with maybe a light shower. Highs today a little below normal, in the 60s. Zonal flow aloft behind the front tonight into Wednesday. Light flow in the lower levels will keep the morning cloud cover from being very widespread. Even with the sunny skies, the air mass over the area is not very warm and what little flow there is in the lower levels is onshore. Highs Wednesday again the in the 60s. Lows tonight will be a little cool over the Southwest Interior, lower 40s, with mid to upper 40s for the remainder of the area. Weak upper level ridge building Wednesday night into Thursday in response to a large cool upper level low beginning to move southeast out of the Gulf of Alaska. Low level flow remaining onshore. 500 mb heights peaking only in the mid 570 dms. Thursday looks to be the warmest day in the next week with highs in the mid 60s to mid 70s. Lows Wednesday night in the 40s. .LONG TERM /FRIDAY THROUGH MONDAY/...Extended models continuing to be consistent showing large cool upper level low approaching Western Washington Friday with the low moving overhead for the weekend. Weak front spinning out of the low moving through Friday. Right now Saturday looks to be the coolest and wettest day with the low right on top of the area. There is a 20 to 30 percent chance highs Saturday don`t get out of the 50s, over 10 degrees below normal. Low starts to drift southeast Sunday with the flow aloft becoming northeasterly. This could help reduce the amount of showers for Father`s Day especially in the afternoon. Temperatures will remain cool with highs only in the upper 50s to mid 60s. Upper level low moving off to the east Monday with a weak broad upper level trough over Western Washington keeping a chance of showers in the forecast and highs below normal, in the 60s. Felton && .AVIATION...Increasing westerly flow aloft ahead of an incoming shortwave trough. Conditions are mostly VFR across the area terminals this morning as a frontal system traverses the region, though a few spots of MVFR and IFR persist along the coast and southern interior. Latest radar shows showers moving across the interior this morning for some light rain. Widespread MVFR to occasional IFR conditions are expected along the coast through the morning, with high- end MVFR to VFR expected for terminals in the interior. Ceilings will lift some this afternoon, with breaks in the clouds possible by this evening. Weak post-frontal convergence over southern Snohomish County does look to develop and move southward and could keep ceilings locally lower across the central Sound through this evening into the early overnight hours. Stratus looks to redevelop across the interior overnight, however expect conditions to remain VFR for now. S/SW winds persist at 10-15 kt across the region, with gusts up to 25 kt at times as the front moves through. Winds will switch to northerly through the interior this afternoon in association with the westerly push through the Strait and remain northerly through the remainder of the TAF period, through decreasing to 6 kt or less this evening. KSEA...Ceilings remain primarily VFR this morning, though may dip down into MVFR with light rain at times as the front moves through. Cloud cover should break up this afternoon, though weak convergence north of the terminal may keep ceilings locally lower at times this evening and will likely keep ceilings from completely clearing out. Winds S/SW winds up to around 10 to 15 kt, with gusts to 20 to 25 kt possible. Winds will shift to the N this afternoon between 00-03Z, then decrease this evening. LH/SB && .MARINE...Increasing southerly winds across the coastal waters early this morning as a weak frontal system traverses the region today. Winds will reach Small Craft Advisory criteria across the coastal waters briefly this morning, as well as through the northern-most portions of Puget Sound. Following the frontal passage this afternoon and into tonight, west winds will push through the Strait of Juan de Fuca and into the northern portions of Admiralty Inlet at times, permitting additional Small Craft Advisories through late tonight. Onshore flow will continue through the end of the week and into the weekend. Another frontal system will move through the region Friday and Saturday. Several rounds of westerly pushes down the Strait of Juan de Fuca are expected through this time period, some of which may require additional headlines. Seas 4 to 6 ft will build up to 12 to 15 ft by tonight, allowing the SCA to continue through Wednesday morning for the coastal waters. Seas remain at around 6 to 8 ft through the end of the week and into the weekend. LH && .CLIMATE...High temperatures below 60 in Seattle are infrequent the last half of June with 40 occurrences in 79 years of records at Seattle-Tacoma airport. Almost half of them, 17, occurred in the first 20 years. We have had a high below 60 in the last half of June in Seattle the last two years, both on June 17th. Last year the high on the 17th was 59 and in 2022 it was 57. In July there have only been 15 days with highs less than 60 degrees. The high of 58 on July 3rd in 2022 was the only time it has occurred in the last 20 years. Highs in the 50s are even rarer in August with only 9 occurrences at Seattle-Tacoma airport. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 2 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory from 11 AM this morning to 2 AM PDT Wednesday for East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory from 11 AM this morning to 5 AM PDT Wednesday for Coastal Waters From Cape Flattery To James Island Out 10 Nm-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 until 8 AM PDT Wednesday 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. && $$