textproduct: Seattle/Tacoma

SYNOPSIS

A strong early-season system will bring rain and gusty winds to western Washington Wednesday into Thursday. The deep upper level low lingers over the Pacific Northwest through the weekend for continued cooler and unsettled conditions.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

Plenty of stratus in place across of much of western Washington this afternoon. Satellite imagery shows the incoming storm offshore, with the warm front approaching the coastal waters and the cold front just behind it. The parent low is located off the coast of the Alexander Archipelago. This warm front will reinforce some moisture and bring chances for isolated showers tonight, but most locations should remain mostly dry. High temperatures this afternoon reaching the mid 60s to low 70s.

The cold front will begin to approach the coast early this morning and slowly move across western Washington throughout the day. Winds will start to increase tonight with a push of southwesterlies through Puget Sound and Hood Canal that will eventually make its way to the north interior by early Wednesday morning. South to southeasterly winds will also increase along the coast early Wednesday morning. Winds will peak across the area as the frontal system moves from northwest to southeast, so first along the coast late morning then across the interior in the afternoon. Maximum wind gusts across the aforementioned areas look to reach up to 35-40 mph, where Wind Advisories have been issued. Elsewhere, gusts up to 25-35 mph are the most likely scenario. Full foliage on the trees may cause more widespread impacts that would otherwise be expected in the winter when trees are bare. Localized power outages and downed trees will be possible. Winds will be slow to ease overnight before really easing Thursday morning.

The main bulk of the rain will begin to arrive along the coast this morning then moving across the interior in the afternoon. The coast and Olympic Mountains will get the most precipitation, with forecast amounts remaining in the 1-2" range by Thursday morning. Forecast amounts have gone down slightly for the interior and Cascades with stronger rain-shadowing effects and the more southerly track of the cold/occluded front across the area, losing the some of the orographic enhancements in the mountains and focusing the strongest onshore moisture transport farther south. Amounts of around 0.25-0.75" are forecast, with around a 40% chance of seeing 0.5" at SeaTac airport.

Behind the frontal passage, most notably along the coast (15-20% chc), there will be a chance for thunderstorms Wednesday afternoon.

As the fronts move south and the low pressure center moves down near the coast on Thursday, showers will continue across the area. There will also be a 15-20% chc of thunderstorms, with the best chances across southwestern WA and areas south of the Seattle metro/Olympic Mountains.

LONG TERM /FRIDAY THROUGH TUESDAY/

The upper level trough that has been supporting this weather system will reach the Pacific Northwest by Friday and essentially remain overhead through the weekend. This will maintain chances for showers and low chances for thunderstorms in the afternoon each day. The day with the best chances for thunderstorms will be Friday, mainly along the southern WA Cascades. Model solutions begin to diverge greatly going into next week as models try to figure out how or if to progress the trough off to the east. The operational runs are pushing troughing off to the intermountain west, but we still remain under their influence and chances for rain remain in the forecast. Quite a few ensemble members (about 55% of members), however, are bringing in some upper level ridging for the beginning of next week which would keep conditions warmer and drier. The NBM mean forecast shows temperatures near climo and broadbrushed slight chances for showers.

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AVIATION

A mix of VFR and MVFR cigs this afternoon as some terminals continue to struggle to scatter out. VFR conditions expected for interior terminals the rest of today. Along the coast, deteriorated ceilings will continue into Wednesday. High-end MVFR is possible (30-40%) for the interior terminals Wednesday morning, with highest chances to likely see MVFR for the Kitsap Peninsula. Breezy conditions will develop this afternoon, with gusts generally around 20-25 kt. Stronger winds are expected after 06z Wednesday first along the coast and fill in across the interior through the morning. These stronger winds will persist through Wednesday afternoon. The strongest winds are expected along the coast, north of PAE, and southern interior, with gusts 35-40 kt. As for the other terminals, gusts will be around 25-30 kt. Winds will gradually subside throughout the evening hours on Wednesday.

Rain will arrive at the coast Wednesday morning and will reach the interior terminals by the afternoon. Additionally, there is a 20% chance of thunderstorms along the coast, Olympic Peninsula, and Cascades on Wednesday. Elsewhere, chances for thunderstorms are around 10-15%. Gusty/erratic winds, heavy downpours, and constant lightning will pose a threat within thunderstorms.

KSEA...VFR conditions today. Models continue to highlight the chance (25%) for high-end MVFR Wednesday morning. Breezy winds SW this afternoon with sustained speeds 10-12 kt and gusts up to 20 kt. Stronger winds expected Wednesday morning after 12Z and lasting through the afternoon hours, with gusts to 25-30 kt. Winds will gradually subside throughout the evening hours. There is a slight chance (10%) of thunderstorms Wednesday afternoon.

MGF

MARINE

A low pressure system will begin to work its way across the region starting tonight. The cold front will move through on Wednesday with the low center moving down through the waters on Thursday. Winds will increase tonight across the region late tonight. Despite sustained winds falling just short, wind gusts remain likely (60- 90%) to reach gale force across most of the coastal waters, and through the northern Salish Sea from Admiralty Inlet up through the East Entrance and into the Northern Inland Waters. Wind gusts through the Puget Sound and Hood Canal look to begin to increase as early as tonight and reach Small Craft Advisory criteria and will continue through much of the day tomorrow. Portions of the central Strait of Juan de Fuca south and east of Victoria may also see Small Craft to gale force gusts, but the majority of the zone should stay sheltered from the strongest winds. The strongest winds area-wide should start to decrease following the frontal passage Wednesday night, but additional headlines may need to follow overnight into Thursday morning as winds look to stay elevated before finally easing by Thursday afternoon. Broad low pressure will remain over region through the end of the week into this weekend though winds look to remain light.

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

Seas 4-5 ft increasing tonight to 7-9 ft before peaking Wednesday afternoon, in conjunction with the winds, up to 9-12 ft from the south. Waves ease a bit late Wednesday before westerly swell arrives on Thursday, pushing seas back up to around 10 ft. Seas ease to around 4-6 ft by Thursday night and remain like so through 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 to the coast and Olympic Mountains, with 1-2" possible there. Elsewhere, amounts will be lower but most areas should see a wetting rain. 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, or up to 40 mph under areas with a Wind Advisory. Chances for showers and thunderstorms will continue Thursday into this weekend, 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-Lowlands of Western Whatcom County-Port Townsend Area-San Juan County.

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

PZ...Gale Warning from 2 AM to 11 PM PDT Wednesday for Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca- Northern Inland Waters Including The San Juan Islands.

Small Craft Advisory until 11 PM PDT Wednesday for Puget Sound and Hood Canal.

Gale Warning from 11 PM this evening to 5 PM PDT Wednesday 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.