textproduct: Seattle/Tacoma

SYNOPSIS

A strong frontal system will bring additional precipitation this evening with the trailing low pressure moving onshore and advancing inland overnight. Expect gusty winds near the low with moisture diminishing Friday morning. High pressure then builds over the region with a gradually cooler and mostly drier trend, though a few weak disturbances arrive Saturday and Monday night.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

After a bit of a lull this morning between the rounds of precipitation, it's going to be a damp end to the Thanksgiving Day holiday as the next round of rain is filling in across Western Washington. The associated cold front is pushing into the coastline early this afternoon with the trailing low pressure still offshore entering the coastal waters. Snow levels are starting off at around 4500 ft or so across the region and will remain somewhat high while the moisture streams across the region. Expect showers to taper from northwest to southeast overnight and through the morning Friday as the low advances onshore somewhere south of Grays Harbor or near the mouth of the Columbia River. Ahead of this low, expect to see some gusty winds this evening, with some gusts into the 30-35 mph range across the coastline and into the interior through the Chehalis valley. Winds will ease as the low continues to push southeast inland and continue to weaken.

High pressure then builds over the northeastern Pacific through the day Friday, with the air mass beginning to dry out. Ensemble guidance does vary a bit with the strength, and likely keep it positioned such that a passing impulse Saturday will bring some additional clouds and perhaps even some light rain. We'll also see a gradually cooling trend with overnight lows dipping a few degrees cooler each of Friday and Saturday night. Saturday night may bring widespread temperatures into the lower 30s around the lowlands of Western Washington. 12

LONG TERM /SUNDAY THROUGH THURSDAY/

High pressure again in place on Sunday with the shortwave quickly passing through the flow. This will maintain cooler but dry conditions across the region, with another chilly start Monday morning. Decent agreement in the ensemble guidance suggesting another weak disturbance may be able to push through late Monday night into Tuesday, perhaps again bringing some light mountain snow and lowland rain. Accumulations of both are rather low and not particularly unusual or impactful for this time of year. Even with this passing disturbance, the ridge is likely to rebound for another few days of drier conditions in place across the region. 12

AVIATION

The transition to largely easterly to in some places, variable, winds has occurred early this afternoon. Additional rain activity is moving into the coastal terminals right now, with gusty winds still in the forecast up to 30kts through the rest of the afternoon. More widespread rain is expected across western Washington late this afternoon and will linger through the overnight hours. Expect widespread MVFR to IFR cigs within the heaviest bands of rain. Moist conditions may favor some early morning fog development in the Chehalis Valley and portions of southern Puget Sound tomorrow morning. Given the continued presence of upper level clouds, confidence in a widespread fog event is low, but cannot be ruled out in the most susceptible areas.

KSEA...VFR at the terminal early this afternoon, with light northerly to northeasterly winds. A period of elevated east/northeast winds between 8-10 kts will be favored from 03Z to 08Z. Rain will fill into the terminal generally after 00Z and last through 10-12Z. ENE winds are to continue throughout the period. As stated above, the fog threat for SEA is not as likely as areas south given the persistent cloud cover overnight, but will monitor for potential in future TAF issuances.

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MARINE

.A strong low pressure system continues to move through the coastal waters this afternoon with a cold front pushing onshore. The low will track onshore this evening between Grays Harbor and the mouth of the Columbia River tonight before shifting inland and weakening. With this path, expect backing winds from S/SE to N into the evening hours. While widespread gales are not expected, occasional gusts to 35 kt will likely develop ahead of and south of the low track. Seas will also build to around 11 to 15 ft and remain rather steep with dominant periods initially around 8 to 9 seconds.Winds will also remain enhanced through the western and central portions of Strait of Juan de Fuca. Winds ease by early Friday, with seas subsiding through the day. High pressure then rebuilds this weekend and into the start of next week, and offshore flow will develop over the waters. 12

HYDROLOGY

A passing frontal system and associated low will bring one last push of heavier rain across the region this evening into early Friday. Snow levels will remain above 4000 feet, leaving the majority of the precipitation falling as rain. With expected rainfall amounts holding steady and topping out mostly in the 2 to 2.5 inch range with this system, confidence is increasing that we will not see any river flooding impacts. After tonight, there is no additional hydrologically significant precipitation expected through the next seven days. 12

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 4 AM PST Friday for Central U.S. Waters Strait Of Juan De Fuca-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-Grays Harbor Bar-West Entrance U.S. Waters Strait Of Juan De Fuca.