textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridging progress off and away on Thursday as troughing develops over the Pacific Northwest late this week. An upper low progresses across the region over the weekend bringing rain potential and cooler temperatures. Drier conditions are expected on Monday with a slow warming trend through midweek.

SHORT TERM /TODAY THROUGH SATURDAY/

The upper-ridge that brought slightly above average temperatures yesterday has progressed off and away well east of the Cascades this morning. An upper-trough is now replacing it as low-level onshore flow increases across western WA. The flow reversal is readily apparent on satellite as of 0900z with marine stratus snaking through the Strait of Juan de Fuca. As a result, areas of stratus and cooler temperatures are in store for today. High temperatures are to remain in the lower to mid 70s across the interior, 5-10 degrees cooler compared to the previous day's with coastal areas in the 60s. Zonal flow in the 850 mb levels will lead to weak convergence later tonight across Snohomish County. Overnight lows are to range between the upper 50s to mid 50s.

Troughing further deepens Friday as an upper-low develops offshore of Vancouver Island. Areas of drizzle may also exist Friday morning associated with widespread stratus, however, Friday is expected to remain predominantly dry with the upper low well offshore. PoPs will increase on Saturday across the CWA as the upper-low moves onshore with widespread rain and showers. There is also a 15 to 25% probability of thunderstorms south of Snohomish County Saturday afternoon. Can't rule out locally breezy wind at times. Highs for both Friday and Saturday both in the 60s with lows in the 50s.

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

The upper low continues to drift eastward on Sunday, with a slow drying trend during the evening. The exception being the Cascades where lingering moisture is expected at least through Sunday AM. An upper ridge begins to build well offshore Monday for a slow warming trend. Predominantly dry conditions are then forecast into the middle of next week, but will need to monitor the existence of any weak troughing around the Tuesday timeframe as indicated by a small subset of ensembles. Either way, temperatures trend back to near normal early next week.

AVIATION

Generally VFR across western Washington early this morning, with deteriorated MVFR to IFR conditions expected around 12z-14z as a frontal system brings a marine stratus layer inland. Low ceilings may linger into the early afternoon today, expected to erode for most inland terminals by 21z to reveal VFR conditions. Northerly surface winds will generally remain light 10 kt or less through the TAF period. Another marine push will likely bring another round of MVFR low stratus across the region Friday morning.

KSEA...MVFR conditions expected to develop over the terminal by 13z- 15z this morning as a marine push brings in low stratus. Conditions will likely remain deteriorated through the early afternoon, estimated around 20z-21z. Conditions will return to VFR thereafter, with another potential marine push early Friday morning bringing another round of low end VFR or MVFR ceilings. Winds will remain northerly around 5-10 kt throughout the day, flipping southerly Friday morning around 9z-12z.

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MARINE

A frontal system will continue to cross area waters today, bringing breezy westerlies through the Strait of Juan de Fuca and elevated waves offshore. A Small Craft Advisory remains in effect for the Central and Eastern Strait of Juan de Fuca through the morning, and a Small Craft over the outer coastal waters for waves of 8 to 11 feet and steep seas with a period of 8 to 10 seconds will continue through Friday morning before seas begin to subside.

Another weather system is on track to cross the waters late Friday in to Saturday, bringing little in the way of wind but will generate scattered thunderstorm activity mainly over the coastal waters. Seas will ease by Saturday to around 4 to 6 feet, where they will remain into early next week.

Surface high pressure is expected to build over area waters by the end of the weekend, maintaining generally benign conditions.

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FIRE WEATHER

A weak and mostly dry frontal system passing over the region has brought a return to onshore flow, maintaining cooler and more moist conditions throughout the weekend. Light precipitation is likely late Friday into Saturday as another weak system moves over the region. Conditions are expected to gradually warm and dry into next week, though fire weather concerns remain low at this time.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 8 AM PDT this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 5 AM early this morning to 5 AM PDT Friday 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.