textproduct: Seattle/Tacoma

SYNOPSIS

Lingering showers mainly over the higher terrain will taper off overnight. Precipitation will return to the area Tuesday, with lowland rain, and mountain snow through Tuesday becoming mostly rain through the day Wednesday. Unsettled weather is expected through the holiday and into the weekend with periods of precipitation and cooler conditions.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

Western Washington is experiencing a brief break between systems tonight. The next in a series is slated to bring a rather wet day to the region on Tuesday as a slow moving system gradually lifts a warm front northward over the area. Impactful snowfall is expected in the passes before turning to a wintry mix Tuesday night into early Wednesday. A relative lull in precip is still expected on Wednesday before the next system arrives Wednesday night into Thanksgiving Day. Ensembles have a shown a considerable spread in solutions with this system in terms of strength, but a look at recent model runs suggests that the secondary system will come in vertically stacked. And in the absence of any jet support, it's looking less likely that this system will be impactful in terms of winds. It will, however, be a traditionally wet Thanksgiving. Previous discussion follows with update to the aviation portion. 27

Lingering showers, mainly over the higher terrain will taper off overnight, aided by a brief period of short wave ridging. A stronger system will approach the Pacific Northwest Tuesday, with widespread precipitation beginning to move onshore during the morning. Snow levels will begin the day Tuesday 1500 to 2000 feet with snow accumulations as precipitation moves into the area - particularly through the Cascade Passes. 8 to 10 inches is possible at all of the Cascade passes before snow levels begin to rise Tuesday evening. In addition there is a chance of a wintery mix at Snoqualmie Pass during the evening hours as warmer air rides over cold easterly flow in the pass, with a 30% chance of freezing rain for a period before the pass transitions over to rain later Tuesday night.

Snow levels should rise to well above 5000 feet by midday Wednesday with precipitation transitioning to rain for all but the higher ridges and volcanos. Ensembles continue to highlight a trailing system setting up a second surge of moisture with a warm front later Wednesday afternoon into to the evening. Snow levels will remain generally above 6000 feet, with the heaviest precipitation - mainly rain over the coast and Olympics Wednesday night.

LONG TERM /THURSDAY THROUGH MONDAY/

The trailing system is expected to move into the coastal waters. Ensemble guidance at this point in good agreement at the cold front moving onshore through the day Thursday with the associated surface low moving onshore somewhere along the Washington coast to the west coast of Vancouver Island in British Columbia. The approaching surface low and its landfall will result in some breezy to gusty winds - most likely along the coast. The nature and location of the strongest winds will depend ultimately on the track of the low, and this will be one of the details going into the Holiday that will be monitored. Temperatures should cool somewhat behind the cold front into Friday, with snow levels dipping back down to around 3500 feet.

Ensemble mean forecast suggest some degree an upper level ridge settling in over the Eastern Pacific Saturday into Sunday - setting up the Pacific Northwest for a cool north-to northwest flow aloft and some possibility of weak system brushing the area late in the weekend.

AVIATION

Westerly flow aloft will continue into Tuesday as a warm front gradually lifts northward toward the area. High and mid level moisture will increase overnight ahead of this system. Brief clearing this clearing allowed for the formation of areas of LIFR across portions of the Southwest Interior this evening, but this is expected to dissipate overnight. Ceilings will deteriorate regionwide on Tuesday morning with widespread low MVFR or occasional IFR in rain persisting into Tuesday night.

KSEA...Ceilings will likely straddle MVFR thresholds overnight before lowering to low MVFR or occasional IFR by mid-morning Tuesday in rain with surface visibility of 3-5SM at times. Said conditions will persist throughout the day tomorrow. Surface winds light southerly this evening backing to east/southeasterly 6 to 10 knots on Tuesday morning. 27

MARINE

A frontal system is expected to pass over area waters, bringing increased winds to area waters starting Tuesday morning. Winds for the coastal waters, east entrance of the Strait, and Admiralty Inlet are likely to meet small craft thresholds for which a Small Craft Advisory has been issued. Low-end gale gusts possible at times for the outer coastal waters Tuesday morning. Seas with this system will build to 7-11 ft by Tuesday afternoon, with the highest waves for the outer coastal waters.

A stronger system on Thursday will bring another round of elevated winds and waves. Latest guidance highlights a 50-70% chance of gusts exceeding 21 kt for the coastal waters and Strait of Juan de Fuca. In addition, guidance suggests seas will build to 13-17 ft Thursday evening.

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HYDROLOGY

A stronger weather system will move into Western Washington late Tuesday, with continued precipitation at times through Thursday. The storm total precipitation are higher today but there remains uncertainty in the QPF among models. Rivers will rise as a result of the steadier precipitation, especially for rivers off the central and southern Cascades, as well as the Olympics. Snow levels will also rise to 5500 to 6500 feet by late Wednesday. At this time, the Skokomish River in Mason County is the primary river being monitored for river flooding by Thursday. The potential is there and as such a Flood Potential Outlook for Mason County. Current rainfall and river forecasts indicate a crest on the Skokomish right around flood stage. This, as well as other rivers, will continue to be monitored.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory from 10 AM Tuesday to 4 AM PST Wednesday for Cascades of Pierce and Lewis Counties- Cascades of Snohomish and Northern King Counties-Cascades of Southern King County.

PZ...Small Craft Advisory from 8 AM Tuesday to 1 AM PST Wednesday for East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 10 AM to 10 PM PST Tuesday for Admiralty Inlet.

Small Craft Advisory from 4 AM Tuesday to 1 AM PST Wednesday 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.