Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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411 FXUS66 KSEW 161605 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 905 AM PDT Sun Jun 16 2024 .SYNOPSIS...Showers and isolated thunderstorms will continue today as an upper level trough remains over the region. The trough will shift east on Monday with lingering showers over higher terrain. A warming and drying trend will commence for the remainder of the week as high pressure aloft gradually builds into the region. && .SHORT TERM /TODAY THROUGH TUESDAY/...
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Upper trough remains over the region, but instability will be somewhat less today as temperatures gradually warm aloft. Flow at the surface and aloft is weak, so showers that do form today will be slow movers. Current forecast looks on track. 27 As of 2 AM PDT, convergence zone showers between Snohomish and Stevens Pass are slowly tapering off. Rain rates have lessened with these showers, and the Flash Flood Watch for the Bolt Creek burn scar has been allowed to expire. Alongside the convergence zone activity, light showers along the coast will continue to progress inland with onshore flow while showers just north of the Canada border continue to shift southward with an advancing front. An upper level trough will slowly drop southward throughout the day today, swinging a frontal system across western Washington. Another round of showers will spread southward throughout the day with embedded thunderstorm activity mainly southwest of the Puget Sound, where models show instability peaking around 250-300 J/kg in the early afternoon. Storms that develop may produce small hail, locally heavy rain, and gusty outflow winds alongside lightning. The primary push of moisture will taper off by this evening, with another round of showers mainly over higher terrain moving southward across western Washington early Monday morning as a disturbance in the northerly flow aloft ripples through. Conditions will dry out for most areas on Monday, except for light showers favored to linger over the North Cascades. Another shortwave trough will drop across the Pacific Northwest early Tuesday, stirring up more light shower activity once again favored over the mountains. Temperatures will remain on the cool side in the mid 60s today and Monday before returning to near- normal around 70 degrees by Tuesday. .LONG TERM /WEDNESDAY THROUGH SATURDAY/...Ensembles continue to highlight weak flow through the extended period with a warming trend through at least mid-week. Onshore flow will keep coastal areas cool while lowlands further inland are on track to reach 80 degrees by Thursday. Temperatures will slowly moderate thereafter with mostly dry conditions through the period. Lindeman
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&& .AVIATION...
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A broad upper level trough remains over the Pac NW with a cool and slightly unstable air mass over western WA - with additional showers expected. Ceilings are a mixed bag with pockets of MVFR conditions. The trend is for most areas seeing VFR conditions this afternoon. As the upper level low continues to move south and east throughout the day, flow aloft will be variable for much of the day before turning to the northeast by tonight and becoming more northerly Monday. 33 KSEA...MVFR conditions in place this morning and will likely stay that way til around 18Z. Still a little instability expected this afternoon, which will give cigs a boost but will also carry shower chances. PoPs remain low and does not look to be enough instability to warrant any thunder mention in the forecast. Surface wind discussion immediately above this section applies. 33/18
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&& .MARINE...
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High pressure over the NE Pacific will maintain light to moderate onshore flow across western WA this week. Expect a westerly surge through the Strait of Juan de Fuca this evening - a Small Craft Advisory is in effect. Seas generally 4 to 6 feet for much of today before increasing to 6 to 8 feet tonight. These will ease throughout the day Monday, getting back to 4 to 6 feet by Monday evening. 33/18
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&& .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$