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Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
737 FXUS66 KSEW 211604 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 904 AM PDT Fri Jun 21 2024 .SYNOPSIS...A upper level ridge over the region today will shift eastward on Saturday. An upper level trough moving into British Columbia on Sunday will produce cloudier and cooler conditions along with a chance of showers. Weak upper level ridging will bring a modest warming trend and generally dry conditions into the middle of the coming week before another trough arrives for cooler conditions and the return of a chance of showers. && .UPDATE...Mostly clear skies across the region except for the immediate coast where some low marine stratus will erode through the morning. Highs today will reach into the upper 70s to upper 80s across the lowlands. While the predominant HeatRisk values are in the minor/yellow category, there is a decent portion of the urban area that will see moderate/orange HeatRisk levels. Fortunately this heat will be short lived as onshore flow increases this weekend and brings some natural A/C. At this time there are no heat alerts in effect, but it is possible that some heat-sensitive populations could experience affects from the heat. -Wolcott- && .SHORT TERM /TODAY THROUGH SUNDAY/...Much like this time yesterday, mostly clear skies prevail across Western Washington early this morning except for some patchy stratus along the immediate coast. An upper ridge axis will slide eastward across the area later today. 850 millibar temperatures peaking near 14C today suggest a degree or two of warming for most of the interior over yesterday while an increasing sea breeze will hold coastal temperatures near or a little below yesterday`s readings. Increasing low level onshore flow will pull the marine layer into the coast and locally inland tonight. Coastal areas will likely remain socked in with stratus on Saturday, but another day of sunshine is expected for the interior. Falling heights and a seepage of marine air inland will cool temperatures a few degrees on Saturday. The onshore flow really ramps up Saturday night into early Sunday as an upper trough moves onshore over British Columbia. Coastal areas should see some drizzle or light showers Saturday night before the shower threat spreads inland by Sunday morning. QPF remains minimal, but an expected convergence zone should squeeze out a few hundredths of an inch over parts of Snohomish County on Sunday morning. With all of the clouds and spotty precip, high temperatures over the interior lowlands on Sunday will be 10 to 15 degrees cooler than Saturday. .LONG TERM /MONDAY THROUGH THURSDAY/...Just as in previous model runs, the upper trough washes out fairly quickly as it pushes inland early Monday with upper ridging quickly rebuilding across the area. After some morning clouds on Monday, some sunshine is likely to return with high temperatures bouncing back to near seasonal levels. The upper ridge is expected to strengthen as the axis shifts east of the region on Tuesday. This should allow for some further warming. Another upper trough approaching Vancouver Island will begin to assert some influence over Western Washington Wednesday into Thursday with cooling temperatures and a returning chance of some showers. 27 && .AVIATION...High pressure remains in place over the region, moving east through Saturday. Continued westerly flow aloft with light flow in the lower levels becoming onshore tonight into Saturday. This will maintain mostly clear skies area wide, but low stratus and fog will remain along the coast through 17z. Expect a return of coastal stratus to the coast after sunset and again a weak push into the lower Chehalis but unlikely to make it to KSHN/KOLM tonight. KSEA...VFR conditions continue under clear skies through the period. Expect north surface winds increasing to 6-8 kt this afternoon. Surface winds becoming southerly after 12z tonight. && .MARINE...High pressure over the coastal waters with lower pressure inland today. Onshore gradients increasing tonight as weak system approaches the area. System moving through Saturday with increasing onshore flow behind the system Saturday night. Weak surface high pressure over the coastal waters Sunday through Tuesday. Small craft advisory winds in the Central and Eastern Strait of Juan de Fuca tonight. Gales possible in the Central and Eastern Strait Saturday evening with small craft advisory winds in Admiralty Inlet. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Saturday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca. Gale Watch from Saturday evening through late Saturday night for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$