textproduct: Seattle/Tacoma

SYNOPSIS

Additional frontal systems through Thursday will bring continued heavy mountain snowfall at times. An upper ridge will begin to build into the Pacific Northwest Friday, although a frontal system over the weekend keeps precipitation potential in the forecast.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

No major forecast updates have been made this evening. The Winter Weather Advisory for the Olympic Mountains has been allowed to expire this evening as the bulk of the precipitation has shifted east. Convergence zone activity has developed in Snohomish county, for increased snowfall rates in the Cascades. Snow is also ongoing in the central and southern Cascades. Elsewhere, scattered showers are progressing through the area with breezy southwesterly winds expected through late tonight. The rest of the previous discussion can be found below, with an update to the aviation sections. 21

Active weather remains the story tonight as the front looks to get hung up over the area before starting to fizzle out overnight and into the early morning hours Wednesday. A secondary impulse reaching the coast mid-morning however will not allow for much of a break in precip...if any at all...for the area. This impulse will also provide a boost to winds, although speeds and gusts are expected to remain lower than those observed today. Will continue to evaluate the need for another round of wind headlines, but current solutions keep speeds below advisory thresholds. As the large scale upper level trough begins to push eastward Wednesday night minor impulses along the backside will keep precip going...albeit slowly becoming more and more scattered at some point Thursday afternoon. As alluded to above, storm total snowfall for the Cascades has not changed much from prior solutions, thus will keep inherited Winter Storm Warning in place and will allow for the Winter Weather Advisory for the Olympics to run its course. Deterministic and ensemble models all agree on the influence from an upper level ridge starting to work its way into the Pac NW Thursday evening, however it is worth noting that majority of solutions have scattered showers persisting for the remainder of the short term.

Lowland daytime highs will see a slight warm-up from Wednesday into Thursday starting from the lower to mid 40s Wednesday increasing a few degrees to the mid to upper 40s Thursday. Overnight lows will be similar tonight and Thursday night...mainly in the upper 30s to lower 40s, although they do take a bit of a hit Wednesday night, generally in the lower to mid 30s.

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LONG TERM /FRIDAY THROUGH TUESDAY/

Although some lingering precip...especially over the Cascades...will be possible as Friday begins, there is a good consensus that W WA will see increasingly drier conditions throughout the day as the upper ridge shifts further eastward. Consensus starts to fall apart entering into Saturday. While models agree on keeping the first half of the day dry, starting to see differing opinions as to how long this break in the action lasts. Deterministic GFS is the slowest in moving the ridge out...keeping things dry into Saturday night before bringing in the next frontal system. But even that system is short- lived with another ridge behind it to finish out the long term period. Deterministic Euro aligns better with the majority of ensemble solutions, bringing in the next frontal system at some point Saturday afternoon and returning the area to an active weather pattern with precip in the forecast for the remainder of the long term. ECMWF does try to hint at a minor ridge for Tuesday, however this feature does not appear to be strong enough to do much along the lines of scouring out moisture already in place. NBM does its best to split the differences, however might be a touch on the optimistic side, keeping PoPs in the low-end Chance, high-end Slight Chance categories...as good a solution as any at this point until a more convincing consensus can emerge.

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AVIATION

Breezy southerly to southwesterly winds are ongoing across most terminals due to the front being hung up in western Washington. Gusts should begin to die down after 06Z for most terminals, but potentially remain elevated in portions of Puget Sound, but remain southerly through the overnight period. Cigs are mixed between MVFR and VFR and will remain there overnight. Terminals such as KPWT and KOLM could see periods of IFR to LIFR early tomorrow morning (12Z), and again between 15-18Z as more rain enters the area. Southerly gusts up to 20 kts are also favored tomorrow morning as the rain begins again.

KSEA...MVFR at the terminal with a continuation of southerly gusts up to 25 kts. The high resolution model guidance is more aligned with keeping gusts in the TAF overnight. The average speed converges on around 23 kts, which appears to be the most sensible solution given the pattern. There is a 1 out of 10 chance that gusts could reach 30 kts. There is a 50-60% chance of cigs as low as 1500 ft AGL beginning at 14Z for SEA, lasting until 18Z as the next round of rain moves into the area.

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MARINE

Winds will remain breezy across the area waters tonight in the wake of the frontal system that pushed across the waters this afternoon. A push of westerly winds is likely along the Strait of Juan de Fuca into Wednesday in its wake. While occasional gusts to 35 kt will be possible at times across the central Strait, the majority of the winds look to remain between 20-30 kt at this time.

Another frontal system will move across the area Wednesday into Thursday and will likely bring another round of small craft southerlies to the area waters. High pressure will then build in its wake on Thursday and will persist into Friday, however could see a weak system move into the region again over the weekend.

Seas hovering between 10-12 ft today will build towards 20-22 ft Wednesday. Large seas will linger into Thursday, before dropping back down to 10-12 ft Friday. Seas look to increase to 13-16 ft again over the weekend as the next system approaches the area waters.

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HYDROLOGY

Steady precipitation is becoming more showery in the wake of a frontal system that passed through the region. Liquid amounts over the Olympics of around 1.5 inches from this system will allow rivers like the Skokomish to continue to rise through this evening and potentially come close to Minor Flood Stage. As a result, a Flood Watch remains in effect for Mason County for the potential flooding on the Skokomish River.

Snow levels around 3500 feet will fall to 2500 ft tonight into Wednesday. While additional precipitation is expected Wednesday into Thursday with another frontal system passing through the region, the lowering of snow levels and progressive nature of the system will help mitigate further flooding concerns for the river by Wednesday morning.

For the remainder of area rivers, no flooding is expected over the next 7 days.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Coastal Flood Advisory from 5 AM to 11 AM PST Wednesday for Lowlands of Western Whatcom County-San Juan County.

Winter Storm Warning until 4 PM PST Thursday for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County- Cascades of Whatcom and Skagit Counties.

Flood Watch through late Wednesday night for Foothills of the Western and Southern Olympic Peninsula-Middle Chehalis River Valley-Olympia and Southern Puget Sound-Olympics- Southern Hood Canal-Willapa and Black Hills.

High Surf Advisory from 10 AM Wednesday to 10 AM PST Thursday for Grays Harbor County Coast-Northern Washington Coast.

PZ...Small Craft Advisory until 4 PM PST Thursday 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-Grays Harbor Bar- West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 7 AM PST Wednesday for Central U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 4 AM PST 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 9 PM PST this evening for Puget Sound and Hood Canal.