textproduct: Seattle/Tacoma

SYNOPSIS

A cold front will bring lowland rain and mountain snow today. Weak high pressure will build over the region on Thursday, bringing drier and milder temperatures through this weekend. An upper level trough will bring back unsettled conditions early next week.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

Latest radar imagery shows generally light to moderate precipitation moving across Western Washington this evening as a cold front continues to push eastward this afternoon, bringing lowland rain and mountain snow. A Winter Weather Advisory remains in effect for the northern Cascades with 8 to 12 inches expected. High-res guidance remains consistent with a convergence zone developing this evening in Snohomish County and then gradually drifting southwards towards the Snohomish/King County line, which includes Stevens Pass. Expect higher rain and snow rates along the convergence zone. In addition, an unstable air mass over the region will bring a slight chance (10-20%) of isolated thunderstorms to the region today. Behind the cold front, expect precipitation to turn more showery in nature. Isolated showers will continue into the first past of Thursday, with showers tapering by Thursday evening as weak high pressure beings to build over the region. High pressure over the region will bring a break in precipitation and milder temperatures late in the week. A front will approach from British Columbia on Friday, but will fall apart before making it to Western Washington.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Dry and mild temperatures will continue into the weekend, with temperatures peaking in the mid to upper 50s. On Sunday, an upper level trough over the Gulf of Alaska will slowly descend southwards, marking the return of unsettled conditions to the region early next week. Model solutions begin to differ around the middle of the week. Conditions look to remain unsettled midweek, but there is significant disagreement between the track of an upper level low at this time.

MGF

AVIATION

A shortwave trough will drag a cold front across the terminals this afternoon. The jet stream pattern remains strong-zonal for the flow, with winds out of the west/southwest. Down at the surface, winds will continue to remain breezy out of the southwest with sustained winds 8-12 kt, gusting up to 20-25 kt. The line of showers will continue to track eastward into the mountains, with showers becoming more scattered behind this line later this evening/Thursday. A convergence zone will develop this afternoon in southern Snohomish County, and likely remain within the vicinity of KPAE through tonight (staying north of KSEA and KBFI). There remains a 20% chance of thunder with activity through this evening. Ceilings are likely to remain VFR with the lighter showers/dry periods of the TAF period (expect lower ceilings/visibilities with heavier showers this afternoon down to MVFR and even IFR briefly). Gusty winds will diminish tonight to 10 kt or less out of the southeast/southwest into Thursday.

KSEA...Showers this afternoon will become more scattered through the evening, becoming drier later tonight/Thursday. Ceilings with a heavier shower may dip briefly down to MVFR (as well as visibilities). Otherwise expect VFR conditions with light showers or dry conditions through the TAF period. Breezy southwest winds 8-12 kt gusting to 25 kt will diminish tonight to 10 kt or less out of the south Thursday.

HPR

MARINE

A trough will swing a cold front across the waters this afternoon. The winds behind the front will increase as onshore flow through tonight. Several small craft warnings remain in effect for portions of the interior and coastal waters, and a gale warning for the eastern two thirds of the Strait of Juan de Fuca through tonight. Winds will ease going into Thursday with ridging building over the region inland. This will cause brief offshore flow to finish off the week for most waterways. A weak system will approach Sunday, with a potential for a trough moving over the waters towards midweek next week. Probability of impactful winds remains low going into this weekend/next week for any headlines.

Seas will decrease below 10 ft today, dropping into the 6-8 ft range through the weekend, further decreasing to 4-6 ft next week.

HPR

HYDROLOGY

No river flooding expected in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 5 AM PDT Thursday for Cascades of Snohomish and Northern King Counties-Cascades of Whatcom and Skagit Counties.

PZ...Small Craft Advisory until 11 PM PDT this evening 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-Northern Inland Waters Including The San Juan Islands-West Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning until 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 7 PM PDT this evening for Admiralty Inlet-Puget Sound and Hood Canal.