textproduct: Seattle/Tacoma

SYNOPSIS

Unsettled conditions will persist across western Washington through Monday as troughing continues over the region. A series of strong frontal systems will bring heavy mountain snow, breezy winds, and widespread lowland rain Tuesday through Thursday before an upper ridge builds over the western US.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

A shortwave offshore will continue to spread light shower activity across the interior this evening. Upper level troughing will shift inland tonight into Monday, maintaining scattered showers overnight and into the morning. A cooler air mass will move into the region, dropping temperatures into the 30s overnight and allowing snow levels to lower to 2500 to 3000 feet. Shower activity will taper off Monday afternoon, providing a brief lull before the next incoming system. Major coastal flooding has ceased this afternoon along the Pacific Coast and northern Salish Sea coastlines, with minor to moderate coastal flooding elsewhere. Astronomical tides will continue to lessen from this point, with minor to moderate coastal flooding set to continue over the next few days.

A strong frontal system will cross the region on Tuesday, bringing the next round of significant weather. While winds will become quite breezy as the cold front digs into western Washington, some uncertainty remains over how windy conditions will be. The main story will be snowfall, and with snow levels lowering well below pass level to near 1500-2000 feet, the mountains are on track to see significant snowfall with this system. Forecast models continue to show 24-hour snowfall totals on the order of 1 to 2 feet Tuesday morning through early Wednesday morning, with heavy accumulations through the central Cascade passes. For the lowlands, Tuesday will be a damp and windy day with rainfall totals ranging generally from a half inch to an inch.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Precipitation will briefly taper on Wednesday as the frontal system shifts east of the Cascade crest. Another strong weather system will be right on its heels, bringing another round of heavy precipitation to the region Wednesday through Thursday. This system will likely bring an additional couple of feet to higher elevations of the Olympics and Cascades, bringing storm totals to 3 to 4 feet of snow. A Winter Storm Watch has been issued from Tuesday morning to late Thursday evening as confidence grows over the potential for significant mountain snow. The lowlands will see another round of rain reaching a half inch to an inch during this period.

Forecast confidence decreases towards next weekend as an upper level ridge builds over the western US. Conditions may dry out next weekend, but models continue to show potential for another wet system overrunning the ridge and bringing more precipitation to the region. While a chance of lowland rain and mountain snow remains in the long range forecast, temperatures next weekend will warm up and may reach the low 50s for some areas.

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AVIATION

A surface low remains offshore just west of KHQM this evening, with widespread showers wrapping around through the region. Expect the flow aloft to turning increasingly westerly as the upper trough slides inland tonight. This will maintain scattered showers for most of the region, though a few bands of heavier showers closer to the low center will likely bring heavier rain and lower ceilings/visibility through around 06z near the coast and 06-10z for the southern Puget sound terminals south through KOLM/KCLS. Elsewhere, continued scattered showers and steady lower VFR to MVFR ceilings will remain. Predominantly southerly surface winds this evening, though some variability in direction near the surface low as it tracks inland can be expected.

KSEA...VFR ceilings this evening with scattered showers. Expect a heavier line of rain 06-09z associated with passing low that will bring ceilings/visibility into MVFR range. Expect residual moisture to maintain ceilings around 1500 ft or so into the morning push before gradually lifting through the day.

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MARINE

Weak high pressure will start to build over the waters tonight into Monday, leading to decreasing seas and winds over the area waters. A stronger weather system will cross over the area on Tuesday, leading to increased south/southwesterlies over the coastal waters, along with increased southerlies over the interior waters, likely small craft advisory strength. These winds look to continue through Wednesday.

Surface high pressure looks to build over the area Thursday into Friday which would help marine conditions calm down a bit.

Coastal seas 6 to 8 feet this afternoon decreasing into Monday. Seas will build again on Tuesday, building upwards to the 14 to 18 foot range, with the highest seas being in the outer coastal water zones. These elevated seas will continue through Thursday.

Mazurkiewicz

HYDROLOGY

The Skokomish River is expected to crest this evening just below flood stage and continue to fall into Tuesday morning. It is expected to crest above minor flood stage later Tuesday with additional precipitation entering the region. For the remainder of area rivers no flooding is expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Coastal Flood Advisory from 6 AM to 10 AM PST Monday for Island County-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-San Juan County.

Winter Storm Watch from late Monday night through Thursday afternoon 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.

Coastal Flood Advisory from 5 AM to 9 AM PST Monday for City of Seattle-Downtown Everett / Marysville Area-Eastern Kitsap County-Lowlands of Pierce and Southern King Counties-Shoreline / Lynnwood / South Everett Area.

Coastal Flood Advisory from 11 AM to 3 PM PST Monday for Eastern Strait of Juan de Fuca-Grays Harbor County Coast- Northern Washington Coast-Western Strait of Juan de Fuca.

PZ...None.