textproduct: Seattle/Tacoma

SYNOPSIS

A weather system will move into the region today, bringing lowland rain, mountain snow, and gusty winds to the western Washington. Showers will linger across the Cascades into Thursday before a ridge of high pressure builds back into the region and brings warmer and drier conditions to the area Friday and into early next week. A pattern change is possible by Tuesday as troughing looks to move back into the region.

SHORT TERM /TODAY THROUGH FRIDAY/

The latest forecast remains on track with no updates this morning. A low pressure system dropping southward along the BC coast will swing a frontal system across western Washington today. This system will bring the next round of lowland rain, mountain snow, and gusty winds to the area. Radar this morning is already showing some shower activity moving northward across the region ahead of the system and observations have started to show winds picking up over the coastal waters this morning. Additional details regarding the hazards have been outlined below:

Winds: Expect winds to continue to increase along the coast and the eastern Strait through the early to mid-morning hours. The strongest winds are expected to be along the Pacific Coast and for areas from Whidbey Island northward, including the San Juans, where gusts between 35-40 mph will be possible at times. Elsewhere, winds will be breezy, with winds gusts between 20-30 mph expected as the front moves through. Winds will remain elevated through the early afternoon hours, before easing during the late afternoon and evening. The exception remains along the Strait of Juan de Fuca, where a post-frontal push will keep westerly winds breezy for areas along the Strait this evening and into Thursday morning.

Rain: Showers will continue to move into the area ahead of the frontal system early this morning. Expect more widespread, steady rain to spread inland along the coast between 11-14Z and to make its way inland into the interior between 16-19Z. Steady rain will become more showery in the front's wake, with showers continuing across the area through the evening hours. Overall rainfall amounts remain in the ballpark of 0.25-0.75 inches for areas across the interior and between 0.5-1 inch for areas along the coast.

Mountain Snow: Snow levels around pass level will rise to around 4000-4500 ft by late morning, before falling below pass levels by late tonight. Overall snowfall accumulations for the passes look to remain between 4-8 inches, with the the majority of the snow expected to fall at pass level late this evening and through Thursday morning.

The parent low will then move inland across the region late tonight into Thursday morning. Wrap-around moisture from the low will keep light snow showers going across the Cascades through the late afternoon and early evening hours before tapering. Conditions across the lowlands will largely dry out on Thursday, with a few sunbreaks expected by the afternoon amongst mostly cloudy skies. High temperatures are expected to be in the 50s.

A shift to warmer and drier conditions commences on Friday as a ridge of high pressure starts to build into western Washington. While a weak weather system moving into BC may clip the North Coast and Northern Interior on Friday, expect the majority of the area to remain dry. Afternoon highs will warm a couple of degrees and look to top out in the mid to upper 50s.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Ensembles remain in good agreement with a ridge of high pressure building over the region through the weekend. This will continue to promote a warming and drying trend across western Washington, with afternoon highs expected to warm a couple of degrees each day and to top out in the mid to upper 60s by Sunday. While forecast details become a bit more unclear heading into early next week, ensembles continue to hold on to the warmer trend on Monday as the ridge axis moves inland. At this time, Monday looks like it may be the warmest day across the interior, with afternoon highs expected to approach the upper 60s to near 70 for areas south of the Sound and along the Cascade foothills. Guidance then starts to hint at an upper level shortwave approaching the area by Monday afternoon, but will need to see how this trend evolves in the coming days. Either way, a pattern change looks to arrive by Tuesday as upper level troughing looks to move back into the region.

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AVIATION

South to southwest flow aloft across Western Washington will continue into this afternoon as an upper trough and associated frontal system approach the area. The upper trough axis will shift onshore tonight with the flow aloft becoming east to northeasterly. Ceilings are expected to become primarily MVFR in increasing rain ahead of the front today. A somewhat unstable air mass will follow the front with areas of MVFR ceilings in post-frontal showers continuing into the overnight hours.

KSEA...MVFR in increasing rain is expected through this afternoon. Rain will transition to post-frontal showers after 00Z with MVFR ceilings continuing. Surface winds east to southeasterly 8 to 12 knots into the afternoon will veer south to southwesterly after 00Z rising to 10 to 15 knots with occasional gusts of 20 to 25 knots before gradually easing late tonight.

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MARINE

A weakening surface low around 995 millibars will come ashore near Cape Flattery late this afternoon as an associated frontal system sweeps onshore across Western Washington. Post- frontal onshore flow will follow overnight then weaken on Thursday as weak surface ridging builds across the waters. A surface ridge will largely remain in place into the coming weekend. Thermally induced low pressure expanding northward along the Oregon coast will lead to northerly or weak offshore flow later Saturday in Sunday. A weak system passing north of the waters will lead to a switch to onshore flow on Monday.

Coastal seas 9 to 11 ft this morning will fall to 6 to 8 ft tonight. An additional swell train will arrive on Thursday keeping seas near the 10 ft range before decreasing Friday into the weekend.

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HYDROLOGY

No river flooding is expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 11 AM PDT Thursday for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County- Cascades of Whatcom and Skagit Counties.

PZ...Small Craft Advisory until 4 PM PDT this afternoon for West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 8 PM this evening to 11 AM PDT Thursday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning until 5 PM PDT this afternoon for East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 PM PDT this afternoon for Admiralty Inlet-Northern Inland Waters Including The San Juan Islands.

Small Craft Advisory from 3 PM this afternoon to 11 PM PDT this evening for Puget Sound and Hood Canal.

Gale Warning until 11 AM PDT this morning 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.

Small Craft Advisory until 5 PM PDT this afternoon for Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

Small Craft Advisory until 5 AM PDT Thursday 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.