textproduct: Seattle/Tacoma

SYNOPSIS

Atmospheric river that has been over Western Washington the past few days moving out this afternoon as the cold front that has been stalled over Vancouver Island finally moves through the area. Cooler air mass behind the front for tonight and Saturday. Weak system going by to the north Sunday. Additional weather systems Tuesday and Wednesday. Upper level ridge trying to build Thursday.

SHORT TERM /TODAY THROUGH SUNDAY/

Satellite imagery shows what it has showed for the last few mornings, an atmospheric river over Western Washington. Doppler radar has rain over most of the area with a bit of a rain shadow over the Central Puget Sound. Temperatures at 3 am/10z were in the lower to mid 50s.

Atmospheric river on its last legs with the cold front stalled over Vancouver Island kicking it in gear this afternoon and moving through Western Washington ending the river. Rain most of the day. Breezy conditions developing just ahead and with the front. Decent westerly push behind the front down the Strait of Juan de Fuca late this afternoon. High temperatures will occur this morning with temperatures cooling later this afternoon. Highs in the 50s.

Cooler air mass moving into Western Washington this evening with snow levels dropping to 3500 to 4000 feet. Post frontal showers will decrease overnight. Convergence zone developing over Snohomish county will dissipate overnight as well. Much cooler with Saturday morning lows in the mid 30s to lower 40s.

Not much going on Saturday with zonal flow aloft over the area. Air mass still slightly unstable keeping the threat of showers in the forecast but it will be dry for most of the day. Snow levels continuing to fall bottoming out around 2000 feet. Moisture is limited so not expecting much, if any, new snow in the mountains. Highs colder than the current temperatures, mid 40s to lower 50s.

Much weaker system approaching the north coast Saturday night with the best chance for any precipitation right along the coast. Lows mostly in the 30s. The colder locations could get down to near freezing.

Weak system moving by to the north Sunday giving the area a chance of rain. Highs will remain cool, a couple of degrees either side of 50. Felton

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

Short dry spell Sunday night into Monday with a weak upper level ridge ahead of the next system. Model timing of this feature has been bouncing around between the rain arriving Monday night or Tuesday morning. Most of the solutions are back to the Tuesday morning scenario. This system is associated with a deep 965 mb low. The low is well north in the Gulf of Alaska so not forecasting any impactful winds with the front. Another system Wednesday before an upper level ridge tries to build over Western Washington Thursday. Models currently indicating this could be the start of a small, 3 or 4 day, dry spell. Temperatures remaining a little below normal with highs in the lower to mid 50s and lows in the mid 30s to lower 40s.

AVIATION

Moist west to southwest flow aloft continues across Western Washington today as a frontal system offshore approaches the region. The front will sweep onshore late this afternoon with increasing low level onshore flow in its wake. A weak Puget Sound Convergence Zone may linger into this evening. Widespread MVFR ceilings in rain will continue into early afternoon before turning into post-frontal showers after around 22Z. Some improvement to VFR is expected behind the front late this afternoon and evening, but a few pockets of MVFR may persist in and around convergence zone activity.

KSEA...MVFR in rain is expected through around 21Z before precipitation turns to a few showers behind the front. Ceilings are expected to lift to lower end VFR by around 23Z and continue into the evening. Surface winds southerly 6 to 10 knots will rise to southwesterly 10 to 20 knots with the arrival of the front this afternoon. A transition to N/NE surface winds of 8 knots or less is presently expected to reach the terminal in the 01Z-03Z window this evening.

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MARINE

A front will move onshore later today with increasing onshore flow behind it. A surface ridge will slide eastward across the waters over the weekend. A strong frontal system will reach the waters Monday night into Tuesday.

Coastal seas are expected to remain generally under 10 feet into Monday before a sub-990 millibar low passing over the offshore waters generates another round of double digit seas.

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HYDROLOGY

The end is finally in sight for the atmospheric river over Western Washington. Cold front moving through this afternoon bringing about an end to the river. Even with the river's demise another 1 to 1.5 inches of rain in the Olympics and North and Central Cascades today and tonight. Snow levels will drop significantly behind the front keeping some of this moisture in the mountains in the form of snow overnight.

Flood warnings already out for the Snoqualmie, Snohomish, Tolt Skykomish and Skagit rivers. The Stillaguamish, Skokomish and possibly the Cedar river could be added to this list later today.

Colder air mass moving into the area tonight and Saturday with no hydrologically significant precipitation. Flood crests moving downstream with the upper reaches of the rivers cresting tonight and the lower reaches Saturday. By Sunday all of the rivers are forecast to be back in their banks. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...Flood Watch through this afternoon for Cascades of Snohomish and Northern King Counties-Cascades of Southern King County-Cascades of Whatcom and Skagit Counties-City of Seattle-Downtown Everett / Marysville Area-Eastside- Foothills and Valleys of Central King County-Foothills and Valleys of Pierce and Southern King Counties- Foothills and Valleys of Snohomish and Northern King Counties-Foothills and Valleys of the North Cascades- Foothills of the Western and Southern Olympic Peninsula- Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties- Lowlands of Western Whatcom County-Middle Chehalis River Valley-Olympia and Southern Puget Sound-Olympics- Shoreline / Lynnwood / South Everett Area-Southern Hood Canal-Willapa and Black Hills.

PZ...Small Craft Advisory from 2 PM this afternoon to 11 AM PDT Saturday for West Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning from 4 PM this afternoon to 3 AM PDT Saturday 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 PM this afternoon to 11 AM PDT Saturday for Admiralty Inlet.

Small Craft Advisory until 5 PM PDT this afternoon for Puget Sound and Hood Canal.

Small Craft Advisory until 5 AM PDT Saturday 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.