textproduct: Seattle/Tacoma

SYNOPSIS

An offshore storm system moving into area today will very gradually shift south and east through Monday morning. This will bring widespread rain and breezy conditions through Sunday morning followed by showery unsettled weather into the start of the week. The pattern looks to remain very seasonal for the last week of the month - cooler with a series of systems bringing periods of unsettled weather nearly every day.

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/

The offshore system that has been sliding down the British Columbia coast, has begun to move into the coastal waters of Washington, with light warm frontal precipitation spreading into the north Olympic Peninsula and north interior early this afternoon. This is expected to lift north into British Columbia this evening as the trailing cold front begins to move onshore. REFS guidance showing the cold front slowly moving onshore overnight as the parent system takes it's time moving south and east. Precipitation with the cold front will be heavier that the lighter rain Saturday. While this ultimately is a fairly typical October storm system, it is the first Fall-like system to move into the area, and will definitely feel different as such. Heavier precipitation amounts are expected along the coast and Olympic Peninsula with 24 hour amounts through Sunday evening in the neighborhood of 1-2 inches, and 0.50 to 1 inch along the I-5 corridor eastward. In addition to the rainfall, increasing south winds along the coast this evening will spread inland ahead of and with the front, remaining breezy through Sunday. Peak wind gusts of 20 to 35 mph are possible for many areas.

The parent upper level system is expected to continue its slow south-southeast track through the day Sunday into Monday. Ensembles showing more agreement in the track of the upper level low than the surface low. The higher resolution REFS ensemble hinting at a more northerly track with the ensemble mean showing the surface low moving into Grays Harbor late Monday morning, while many of the other higher resolution ensembles like the HREF and UW ensemble systems show a much more southerly track. In any case, with the upper level low over the area Sunday into Monday morning, scattered, but widespread showers will linger well into Monday before shifting east with the upper level support late Monday afternoon.

High temperatures will trend near normal in the mid to upper 50s, while overnight lows will trend cooler than normal in the in the low 30s to low 40s.

LONG TERM /TUESDAY THROUGH SATURDAY/

The grand ensemble remains generally consistent early in the week with the upper level trough associated with the weekend system shifting into the northern Intermountain area Tuesday morning. Ensembles all hint at a trailing shortwave sliding down the British Columbia coast, with variability in the strength and timing. The consistent message is that the bulk of the relatively light precipitation looks to be focused mainly south of western Washington Tuesday. Ensembles very consistently showing a more consolidated upper level low sliding down the BC coast Tuesday night and into western Washington Wednesday. This looks scenario very similar in many ways to this weekend's system, with cooler temperatures and widespread rain over much of the Pacific Northwest. The pattern looks to remain unsettled Thursday into Saturday with a broad positively tilted upper level trough along the Western US. Some scenarios showing a more consolidate upper level low over California. For the Pacific Northwest the pattern looks to remain unsettled - but seasonal - through the last few days of the month.

AVIATION

Southwest flow aloft increases into Sunday, becoming more southerly by Sunday afternoon as an upper trough digs offshore. Widespread VFR mid and high clouds this afternoon across western Washington ahead of a frontal system. Cigs will lower into MVFR/IFR along the coast and near BLI tonight as rain continues to slowly spread southeastwards. Low-end VFR to high-end MVFR cigs expected for most southern and central Puget Sound terminals by early Sunday. Lower VFR cigs for the afternoon for interior, with continued MVFR for portions of the Olympic Peninsula Sunday afternoon. Vsby reductions possible in areas of steadier rain into Sunday, dropping to 3 to 6SM, lowest along the coast. Increasing S/SE winds for the coast, and E/NE winds for BLI into tonight, remaining light for KPAE to KTCM into Sunday.

KSEA...VFR continues through tonight with mid and high clouds. Cigs slowly lowering towards MVFR by Sunday AM. At this time, the probability for MVFR cigs peaks between 13 to 18z Sunday as rain arrives, with probabilities around 25 to 30%. Rain at times into Sunday PM, with brief reductions to vsbys possible. VFR for Sunday afternoon with continued OVC mid clouds. Light west winds this afternoon, with a light E/NE component tonight into Sunday.

MARINE

A surface low offshore of Vancouver Island will continue to slowly shift southwards along the offshore waters through this weekend before weakening and moving onshore in the vicinity of NW Oregon on Monday. East to southeast winds will increase into tonight ahead of the approaching system. Small Craft Advisory southerly winds continue for a longer duration over the Coastal Waters through at least Sunday afternoon. Gale force wind gusts are also expected at times for the northern outer Coastal Waters through this evening. Southeast winds also increase for the eastern Strait of Juan de Fuca, northern inland waters, and Admiralty Inlet early Sunday. The SCA has been upgraded to a Gale Warning for the east Strait given the higher confidence in gale force wind gusts, along with SCA winds for northern inland waters and Admiralty Inlet. Otherwise, east winds remain elevated for the eastern and western Strait of Juan de Fuca into Sunday. Will need to monitor any additional upgrades to gales, mainly for the far eastern segment of the central Strait. Winds remain light for Puget Sound into Sunday. Winds subside Monday into Tuesday with another system expected to move through the area on Wednesday..AVIATION... Westerly flow aloft will transition southwesterly and increase into tonight as an upper trough digs southwards over the Washington offshore waters. Increasing VFR mid and high clouds today ahead of a frontal system with localized LIFR/IFR over HQM this morning. Cigs may brief fluctuate into high end MVFR at KBLI this afternoon. Cigs slowly lower over the Olympic Peninsula into MVFR/IFR tonight with increasing rain. High end MVFR to low end VFR cigs for Puget Sound terminals Sunday as the frontal system moves across the interior. Vsbys reductions may occur in steadier rainfall over the Olympic Peninsula terminals. Increasing south winds along the coast later today, with light winds for central and southern Puget Sound.

KSEA...VFR conditions through tonight with continued mid and high clouds. Dry conditions into tonight, with rain potential increasing around 12-15z Sunday. Cigs also lowering towards low- end VFR at the onset of the rain Sunday AM. Southeast surface winds becoming more SW this afternoon, mainly less than 5 kts. Surface winds transition back to more E/NE this evening and tonight, remaining light. JD

MARINE

A surface low southwest of Haida Gwaii will shift southward today into tonight and an associated occluded front will clip the coastal waters on Sunday morning. Increasing easterly or southeasterly gradients will lead to small craft advisory winds across the coastal waters as well as the Strait of Juan de Fuca. Seas will build to 10 to 12 feet over the coastal waters late today into Sunday. The surface low is expected to move onshore over northwest Oregon Sunday night into Monday with winds easing and seas subsiding back below 10 feet. Another frontal system will shift southward into area waters on Wednesday.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 PM PDT Sunday for 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 Point Grenville To Cape Shoalwater 10 To 60 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 5 PM this afternoon to 5 PM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 8 PM this evening to 5 PM PDT Sunday for East Entrance U.S. Waters Strait Of Juan De Fuca.

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

Gale Warning until 11 PM PDT this evening for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm.

Small Craft Advisory from 11 PM this evening to 5 PM PDT Sunday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm.