textproduct: Seattle/Tacoma

SYNOPSIS

A strong early season system brings rain and gusty winds to Western Washington Wednesday into Thursday. The deep upper low lingers over the Pacific Northwest into next weekend for continued cooler and unsettled conditions.

SHORT TERM /TODAY THROUGH THURSDAY/

Predominantly dry conditions today with a few showers developing later today ahead of troughing developing offshore. A mix of clouds and sunshine expected with highs in the 60s along the coast and 70s for the interior.

A strong early season system will approach Western Washington tonight with an associated front moving through on Wednesday. This system will bring beneficial rain to the area, with the highest rainfall amounts over the Olympic Peninsula, with some areas exceeding 1-1.50" of rain into Thursday. The bulk of the rainfall will move across Puget Sound Wednesday afternoon through the evening. Rain will then continue at times on Thursday with the deep upper low located offshore. In addition, thunderstorm probabilities increase to 20 to 25% for most of the area by Thursday afternoon, and embedded lightning can't be ruled out with heavier showers.

Winds may be the most impactful aspect to this system on Wednesday given the continued full foliage on trees. At this time, confidence is highest in impactful wind gusts (35-40 mph) along the coast, San Juan Islands, and Whidbey Island. For this reason, a Wind Advisory was issued for these areas on Wednesday, primarily due to the continued foliage and increased risk for downed tree limbs and isolated power outages. Will also need to monitor western Whatcom and Skagit Counties, and the Port Townsend area for further expansion of the Wind Advisory. Elsewhere, wind gusts of 20 to 35 MPH are expected, and localized power outages cannot be ruled out. Winds will peak for most locations during the day on Wednesday before winds ease Wednesday night into Thursday.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

The upper low remains situated over the Pacific Northwest Friday into the weekend. This will result in cooler conditions continuing for Western Washington. Lingering rain showers are also expected to continue at times, although dry periods will exist as well. Probability for thunderstorms remains around 10% Friday and Saturday. Uncertainty begins to increase in ensembles early next week in regards to the timing in which the troughing begins to weaken and drift eastwards. However, a continued troughing influence into Monday likely results in below normal temperatures and the chance for precipitation over the area. JD

AVIATION

South/southwesterly flow aloft continues with persistent upper level troughing offshore. Ceilings under the marine layer remain between MVFR and IFR, elsewhere VFR continues with high clouds overhead. Marine layer clouds will raise to VFR later this morning, through elsewhere mid-level clouds will increase this afternoon as a warm front passes through the area and increases moisture and chances for isolated showers this evening. Heavier precipitation, associated with a cold front, will begin to approach the coast between 09-12Z Wed this evening and slowly move inland, not reaching the interior until after 18Z Wed-00Z Thur. The heavier precip will likely also bring MVFR to IFR ceilings once again and potential limitations in visibility.

South to southwesterly winds will continue to increase through the morning, peaking this afternoon at around 8-15 kts with gusts up to 20-25 kts possible through the afternoon and early evening. Winds will then continue to pick up after 06-12Z Wed, becoming up to 10-20 kt with gusts up to 25-35 kt along the coast and through the north interior.

KSEA...A brief period of IFR conditions this morning under the marine layer, but conditions should improve by 18Z this morning. Otherwise VFR conditions prevail through the remainder of the TAF period, with mid-level clouds increasing tonight. Precipitation will not begin to arrive at the terminal until around 15-18Z Wed. Southwesterly winds will increase this afternoon to around 10-15 kt with gusts up to around 20-25 kt. Winds ease slightly after 09Z Tue but will start to increase once again after 18Z Tue.

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MARINE

High pressure will ease today before a stronger low pressure system begins to approach the coastal waters late tonight. South to southeasterly winds will begin to increase this evening, with winds peaking during the day on Wednesday. Likelihood remains high through the coastal waters (60-90% chc) and through portions of the East Strait of Juan de Fuca, Strait of Georgia, and Admiralty Inlet (50-70% chc) for seeing gale force wind gusts through Wednesday evening. Forecast, however, is having some difficulty latching on to these higher speeds, favoring a zone average that could fall short. As such, left Watch alone for the time being, but did emphasize Gale criteria via gusts in forecast product. This sets the stage for potential upgrade should the aforementioned 60-90 pct chance remain intact. Elsewhere, winds will remain in or just under Small Craft Advisory thresholds. As such, held off on these headlines just yet and figured they'd best be served along with any potential upgrade to the aforementioned Gale Watch.

The cold front will traverse the area waters Wednesday evening, following which winds will begin to decrease. Additional headlines may be needed into Thursday as southerly winds remain elevated through the interior waters from Puget Sound to the Northern Inland Waters. Winds greatly decrease area-wide by Thursday afternoon as the low pressure system weakens and moves southward into Oregon. Broad low pressure will remain over region through the end of the week.

Chances for isolated thunderstorms will pose a threat to the area waters Wednesday and Thursday, through probabilities are marginal (10-20% chc).

Seas 4-6 ft increasing tonight to 7-9 ft before peaking late Wednesday afternoon/early Wednesday evening at 9-12 ft. Seas return to around 6-8 ft Friday into the weekend.

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FIRE WEATHER

Fire weather concerns remain low through the next week. A stronger fall weather system will bring significant rainfall starting early Wednesday, with wetting rains expected area-wide. 1-2" will be possible along the Pacific Coast and the Olympic Mountains. Rainfall may pose a minor threat to highly sensitive and brand-new burn scars. Windy conditions are also expected across the area with gusts ranging from 20 to 35 mph. The bulk of the rain will fall on Wednesday. Chances for showers and isolated thunderstorms continue through the end of the week, but the risk of new starts is lower due to the isolated coverage and the increased fuel moisture from the wetting rains.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 2 AM to 8 PM PDT Wednesday for Island County-San Juan County.

Wind Advisory from 2 AM to 5 PM PDT Wednesday for Grays Harbor County Coast-Northern Washington Coast.

PZ...Gale Watch from this evening through Wednesday evening 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-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands.