textproduct: Seattle/Tacoma

SYNOPSIS

Cloud cover will increase today ahead of an incoming weather system overnight into Friday. Cooler and unsettled conditions will then settle over western Washington through next week as a series of systems maintain chances for precipitation.

SHORT TERM /TODAY THROUGH SATURDAY/

Patchy fog and low stratus have once again expanded along western Washington coastlines this morning under high pressure aloft. Weak high pressure in place over the Pacific Northwest will break down today as the next weather system approaches. Most areas will break out of fog and low clouds by the late morning, but high clouds will continue to increase throughout the day. High temperatures will peak a degree or two higher than yesterday for most inland areas, reaching the upper 40s to lower 50s later today.

A frontal system will move inland late tonight into Friday morning, bringing the next chance for precipitation. Given the limited moisture ahead of the frontal system, precipitation amounts through Friday night will be fairly light. Snow levels will lower to around 2500-3000 feet on Friday, with a few inches of snow accumulation expected through the Cascade passes. Additionally, waves along the Pacific Coast will build to roughly 15 to 18 feet on Friday, and beachgoers should use caution and remain aware of the unsettled seas.

Split flow will begin to develop aloft by Saturday behind another weak frontal passage, allowing precipitation to decrease in coverage. Cooler temperatures will allow snow levels to lower even closer to 2000 feet, but any additional snow accumulations will be light. Temperatures will peak in the mid to upper 40s on Saturday under cloudy skies.

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

Split flow is expected to persist into Sunday, allowing conditions to dry out briefly across western Washington. Sunday afternoon looks to provide some sun breaks ahead of the next incoming weather system Sunday night into Monday.

A deeper upper level trough will drop southward along the Pacific Coast throughout the beginning of next week, bringing in more widespread precipitation and cooler temperatures. Snow levels early next week will fall to around 1500-2000 feet, and while some lowland areas may see some brief falling snowflakes, particularly in the overnight hours, any significant accumulations or impacts are not expected for the lowlands. The mountains, however, will see steady snowfall as this trough digs into the western US, with potential for heavier snow accumulations midweek.

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AVIATION

Light westerly flow aloft will become southwesterly tonight as an upper ridge over the area weakens and a dissipating frontal system approaches the area. Increasing high level moisture has limited formation of fog/stratus thus far, but expect areas of LIFR/IFR stratus and patchy fog this morning. Widespread VFR is expected thereafter under increasing high and mid level moisture. MVFR in light rain showers will develop along the coast after 00Z. Ceilings will deteriorate all areas overnight tonight with widespread MVFR ceilings across the region on Friday morning and light rain developing.

KSEA...Overnight trends suggest chances of LIFR/IFR conditions are waning this morning and will scale back mention of low ceilings and restricted visibility in the 12Z TAF. Otherwise, remaining VFR today with increasing high and mid level clouds. Ceilings will lower tonight and expect MVFR ceilings in areas of light rain after 12Z Friday. Surface winds light southerly becoming S/SW 5 to 7 knots this afternoon.

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MARINE

A weak surface ridge will remain across the waters today. A weak front will move onshore on Friday with a secondary system to follow on Saturday. Surface high pressure briefly builds into British Columbia Saturday night and Sunday turning the flow northerly. A series of troughs digging southward across the coastal and offshore waters will keep conditions unsettled early next week.

Seas will build over 10 feet this afternoon and remain in the 10 to 15 foot range into the early weekend. They may briefly subside below the 10 foot threshold Sunday into early Monday before building back into double digits again as activity offshore generates more long period swell.

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HYDROLOGY

No river flooding is expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 10 AM this morning to 4 PM PST Friday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 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.