textproduct: Seattle/Tacoma

SYNOPSIS

A frontal system will move across Western Washington tonight through Tuesday with increasing rain and breezy winds. Upper ridging begins to build over the Pacific Northwest Thursday and Friday with just a slight chance of precipitation. The upper ridge further builds next weekend for drier, warmer conditions.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

No significant changes made to the forecast this evening. The previous discussion can be found below along with updates to the aviation and marine sections:

Mid and high clouds continue to increase this afternoon across the area ahead of an approaching frontal system. Rain will begin to spread along the northern coast this evening, with rain becoming more widespread for areas north of Snohomish County tonight. The front drifts southwards on Tuesday, with rain moving from north to south by the afternoon. Rainfall amounts will be heaviest across the western slopes of the Olympic Peninsula, Skagit and Whatcom Counties, as well as the Cascades from King County northwards. Generally 1 to 3 inches of rain is expected for the mountains, with 0.50-1.25 inches in the lowlands of Skagit and Whatcom Counties. Significantly lighter QPF from Seattle southwards as the front weakens.

The more impactful aspect to this system will be the increasing southerly winds tonight through Tuesday. South winds are expected to be strongest over western Whatcom County, with gusts of 35 to 45 MPH. Gusty south winds are also expected for the San Juan Islands, western Strait of Juan de Fuca, and a region from Hood Canal to Everett, where gusts of 30 to 40 MPH are anticipated. Elsewhere, winds will be breezy, ranging 25 to 35 MPH. Due to the continued foliage on trees, gusty winds may cause localized power outages and tree limb damage. Winds will slowly subside later Tuesday into Tuesday night for most areas, the exception being a westerly push through the Strait of Juan de Fuca late Tuesday.

An upper ridge slowly begins to build over the Pacific Northwest on Wednesday, resulting in drier conditions. Areas of stratus and morning fog may occur Wednesday AM due to residual moisture at the surface. Temperatures will be cooler Tuesday and Wednesday in the low to mid 60s.

LONG TERM /THURSDAY THROUGH MONDAY/

Zonal flow aloft continues Thursday into Friday. A system will weaken as it approaches Western Washington during this period, resulting in just a slight chance of precipitation at this time, mainly for northern areas. Ensembles are in general agreement in the ridge becoming more pronounced across the Western US this weekend, resulting in drier and warmer conditions. Some uncertainty in the ensembles in regards to the return of more onshore flow early next week, but overall, warmer and drier conditions are expected during this period. JD

AVIATION

Westerly flow aloft will increase overnight as a frontal system offshore moves into the region during the day on Tuesday. Ceilings will deteriorate overnight with rain along the coast spreading into the North Interior late this evening then southward on Tuesday morning. Widespread IFR or low MVFR ceilings in rain are expected to develop 09Z-12Z and persist through much of Tuesday. Gusty southerly surface winds will develop tonight and continue into early Tuesday afternoon. Gusts of 30 to 40 knots are expected from KPAE northward with 20 to 30 knots at times across the remainder of the area.

KSEA...MVFR ceilings expected to develop around 10-12z as rain spreads into the area. Ceilings are expected to become IFR at times toward late morning. Ceilings will marginally improve Tuesday evening as a front gradually shifts east of the area. Southerly surface winds 10 knots will rise to 15 to 20 knots overnight with occasional gusts of 25 to 30 knots between 09Z and 18Z. Winds ease mid to late afternoon Tuesday.

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MARINE

A front approaching the coastal waters will shift inland during the day on Tuesday. Headlines remain in effect for all waters with low end gale conditions expected across the Northern Inland waters later tonight into Tuesday morning. A brief increase in onshore flow will follow the front Tuesday evening before quickly diminishing by early Wednesday. Surface high pressure building over the interior of British Columbia and weak troughing just offshore will lead to some weak east/southeast flow on Thursday. Thermally induced surface low pressure begins to expand northward along the coast toward the weekend for northerly or weak offshore flow across area waters.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 2 AM to 2 PM PDT Tuesday for Lowlands of Western Whatcom County-San Juan County.

PZ...Small Craft Advisory until 5 PM PDT Tuesday for Admiralty Inlet-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- Puget Sound and Hood Canal-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning from 11 PM this evening to 5 PM PDT Tuesday for Northern Inland Waters Including The San Juan Islands.