textproduct: Seattle/Tacoma

SYNOPSIS

Widespread precipitation behind a frontal passage will taper off tonight, with snow showers continuing over the Cascades on Thursday. Drier and warmer conditions will settle into the region over the weekend as high pressure builds overhead, with potential for mostly dry conditions to continue into next week.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

Widespread lowland rain and mountain snow continues this afternoon as a frontal system continues to cross the region. Winds have peaked for the day for most areas, except through the Strait of Juan de Fuca, where elevated post-frontal westerlies will continue overnight. The bulk of the rainfall over the lowlands will shift inland later this afternoon, with showers continuing to stream inland this evening behind the frontal passage. While a lightning strike or two cannot be ruled out in these showers, the likelihood is low. Today will be the coolest day over the next week, with highs peaking several degrees below normal, in the upper 40s to near 50 across the lowlands.

Precipitation will shift mostly eastward of the Puget Sound overnight into Thursday as the parent low pressure center moves onshore over Oregon. A cold front will cross the region Thursday morning, ending most precipitation with lingering light snow showers over the mountains and a Puget Sound Convergence Zone continuing through the afternoon. Temperatures will increase a few degrees on Thursday with some sun breaks by the afternoon.

As high pressure begins to build northward into western Washington on Friday, a weather system will skirt the periphery of the ridge, bringing light rain showers along the northern Olympic Peninsula, Islands, and Northern Interior. Elsewhere, conditions will begin to dry out under cloudy skies with some sun breaks. Temperatures will warm another few degrees into Friday, with highs in the mid to upper 50s across the lowlands.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

High pressure will amplify over the region over the weekend, bringing the warmest temperatures of the year so far to western Washington. Highs will reach the low to mid 60s by Saturday, and continue to warm into Sunday where some areas along the Cascade Foothills and south of the Sound could reach 70 degrees. This also introduces Minor (Yellow) HeatRisk for areas south and east of the Puget Sound over the weekend.

Forecast confidence decreases into Monday, with models shifting the upper level ridge eastward. While ensembles maintain chances for showers early next week, operational forecast models are trending drier with split flow developing aloft. Monday could be the warmest day of the period with many areas seeing highs near 70 degrees, but will have to see how models trend over the next few days.

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AVIATION

South to southwest flow aloft across Western Washington this afternoon ahead of a frontal system will turn easterly overnight then northerly on Thursday as a trailing upper trough axis shifts eastward. A mix of low end VFR and MVFR in rain ahead of the front will become primarily MVFR tonight as a somewhat unstable post- frontal air mass moves onshore.

KSEA...Ceilings are expected to lower to MVFR in rain 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 into Sunday. A weak system passing north of the waters will lead to a switch to onshore flow on Monday.

An additional swell train will arrive on Thursday keeping seas near the 10 feet 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 5 PM this afternoon 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 until 11 PM PDT this evening for Puget Sound and Hood Canal.

Small Craft Advisory until 11 PM PDT this evening 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 PM 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.