textproduct: Seattle/Tacoma

SYNOPSIS

Weak atmospheric river will bring continued rain showers throughout today and into Friday, with the chance of a rain/snow mix early Friday morning. Upper level troughing will keep showers around the area into Saturday. A warm front will then move over the region Sunday into Monday, bringing more widespread rain and keeping the pattern active.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

A weak atmospheric river continues in Oregon, providing western Washington with some widespread showers across the area this afternoon. This weak atmospheric river will lift northward later this evening and into Friday morning, allowing for more moisture to funnel in the area, primarily south of Seattle, although showers will still be present across much of the CWA. A Winter Storm Warning continues for the Cascades and the Olympics as significant mountain snow continues, on the order of a couple of feet for Snoqualmie and Stevens Pass.

Turning into Friday morning, the forecast gets a bit complex and complicated. Cooler air aloft will push down the snow levels downwards to 500 to 1000 feet, which would allow a rain/snow mix to develop across the region. There is usually the question whether moisture will be present, and guidance does show some moisture from the aforementioned atmospheric river still being around the area (especially in the southern half of the state). Latest guidance does suggest there could be light accumulations possible on the higher foothills, along with grassy and elevated surfaces. This is a complex situation as local surface conditions and temperatures will be critical factors in what (if any) snowfall accumulations may be present early Fri morning.

Overall: you will likely see snow in the interior (particularly in Puget Sound) Friday morning in some capacity. However, ground temperatures and near surface temperatures are likely to be above freezing, which will result in highly variable surface accumulation. The places that are likely to see any sort of snow that sticks, are places on the higher foothills, which are likely around an inch or two at best. The time frame for this is generally early Fri morning, (4AM-9AM). After that, daytime heating will take over and warm everything up. Shower will decrease throughout the day, and high temps will be in the low 40s. Heavy mountain snow continuing.

The same problem exists for Saturday morning, although there will be less moisture present across the area. Could see a few flakes fly, but otherwise, Saturday will be a drier day with temperatures in the mid 40s as an offshore ridge builds. Mountain snow will also have gradually subsided by Saturday.

LONG TERM /SUNDAY THROUGH THURSDAY/

Ensembles continue to agree of a warm front will move over the offshore ridge Sunday into Monday, which would bring another round of precipitation over the area. Guidance continues to depict the ridge not being strong enough to keep an atmospheric river from the north out of our area, with lowland rain and a unsettled pattern continuing throughout midweek. A warmer air mass looks to bring up snow levels to 7000 to 8000 feet, along with high temps creeping in the upper 50s, and even lower 60s.

Mazurkiewicz

AVIATION

A strong upper level jet will lift northward, with a stationary front to the south remaining over the WA/OR border. Showers will continue to fall across the terminals through tomorrow, with activity decreasing north to south through the day. Cooler temperatures tonight may lead to some snow mixing in with the rain showers. Probabilities of snow sticking on airport surfaces remains low, though cooler and shady spots may see a few flakes stick briefly overnight. Ceilings and visibilities will deteriorate tonight into Thursday, trending from VFR down to MVFR and IFR. Localized pockets of LIFR can't be ruled out either. Breezy southwest winds 8-12 kt with gusts to 20 kt will diminish to 5 kt this evening, becoming variable under 5 kt tonight and switching to a northerly direction during the day Friday (still under 5 kt). The ensembles have ceilings improving towards MVFR late Friday.

KSEA...Light to moderate rain through tonight, with a chance of a rain/snow mix overnight/early Friday morning. No snow accumulations are expected for the terminal. MVFR ceilings/visibilities this afternoon will likely decrease to IFR later tonight into Friday, with MVFR likely late Friday afternoon/evening. Southwest winds 8-12 kt gusting to 18 kt will decrease to 5 kt tonight, becoming variable late and switching to the northeast on Friday at or less than 5 kt.

HPR

MARINE

A stationary front will remain over the southern coastal waters through the weekend. Precipitation will continue to pass over the waters, with reduced visibilities and ceilings at times. Winds will continue to decrease through the afternoon from yesterday's cold front that passed through. A small craft advisory remains in effect through 5 PM for the Strait of Juan de Fuca for lingering west winds over 20 kt, and the coastal waters through 11 PM for seas above 10 ft. The winds will turn northerly on Friday, with a medium chance on Saturday that gusts exceed 20 kt for the coastal waters. Seas through the weekend will drop and hold around 6 to 8 ft, further decreasing to 4 to 6 ft. A warm front will skirt the outer coastal waters Monday next week, with potential for gusty south winds for the coastal waters, and a few interior waterways. These winds are forecasted to linger into late Tuesday. Seas on Monday will rise to 10 to 12 ft, and linger at those heights through midweek.

HPR

HYDROLOGY

The Skokomish River has crested and will continue to linger in Action Stage. More rain in the forecast through Friday will keep the threat of flooding along the Skokomish Friday into Saturday. With the heaviest precipitation over the Southwest Interior there is also a threat of flooding Friday into the weekend for a few rivers in the Chehalis Basin including but not limited to the Skookumchuck, Newaukum and the Chehalis River from Grand Mound to Grays Harbor. Therefore, a Flood Watch has been issued for those following areas. The flooding threat will ease Sunday into next week for the southern portion of the area. Atmospheric river forecasted to move inland to the north during the first part of next week. If the river ends up a little further south rivers over the northern portion of the area will bear watching the first part of next week.

Felton/Mazurkiewicz

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Storm Warning until 5 AM PDT Saturday 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-Olympics.

Flood Watch from Friday morning through Sunday afternoon for Cascades of Pierce and Lewis Counties-Foothills and Valleys of Thurston and Lewis Counties-Foothills of the Western and Southern Olympic Peninsula-Grays Harbor County Coast-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties-Middle Chehalis River Valley-Olympia and Southern Puget Sound-Olympics- Willapa and Black Hills.

PZ...Small Craft Advisory until 2 PM PDT this afternoon for Admiralty Inlet-Grays Harbor Bar-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.

Small Craft Advisory until 5 PM PDT this afternoon for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 11 PM PDT this evening 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.