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/

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

West-northwest flow this afternoon turning predominantly westerly. Widespread VFR observed so far today (with the exception of KHQM) but ceilings are favored to progressively lower into tonight as a frontal system enters. Rainfall and MVFR cigs will start for KBLI, KCLM, and KOLM between 04-08z and the remainder of interior terminals by 10-12z. Areas of IFR cigs can't be ruled out as well. MVFR/IFR conditions are favored to remain well into the day on Tuesday and possibly into the evening as rainfall gradually tapers.

Windy conditions are also favored throughout the period as the strongest gusts at KBLI could reach up to 35-40 kt between 06-12z Tuesday. Gusts up to 20-30 kt are favored elsewhere overnight Monday into Tuesday. Winds will gradually decrease area-wide by Tuesday afternoon but a westerly surge through the Strait of Juan de Fuca will bring an additional round of gusty winds for KCLM around 20-25 kt.

KSEA...VFR conditions through the evening but cigs will gradually fall. MVFR ceilings expected to develop around 10-12z, as a front brings widespread rainfall. S-SW winds at 5-10 kt this afternoon becoming 10-15 kt with gusts up to 20-25 kt after 06z tonight. Gusts will gradually diminish after 00z Wednesday but lower cigs are favored to remain at this time.

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MARINE

The next frontal system arrives tonight starting at the coastal waters with increasing southerly winds over all waters - Small Craft Advisories are in effect for most waters. The Northern Inland waters have a Gale warning in effect. Winds will turn more westerly through the strait Tuesday afternoon where gale gusts are a possibility for the central/eastern strait. Meanwhile, expect elevated seas with swells reaching 10-11 ft. Onshore flow will ease late Tuesday night. The flow will then turn offshore on Wednesday with a thermal trough along the coast. Light offshore flow continues through the end of the week.

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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.