textproduct: Seattle/Tacoma

SYNOPSIS

A very active pattern is taking shape and will persist throughout the week for western Washington. Periods of heavy mountain snow, lowland rain, gusty winds and possible river flooding are in the forecast.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

Impressively zonal flow over the greater northeastern Pacific will keep the door open for storms to move through western Washington throughout the week. For the rest of today, expect scattered showers throughout the lowlands, with continued periods of snow in the Olympics and Cascades. Tonight into Tuesday morning will likely be the coldest of the week, with snow levels dropping practically to the surface overnight. Anywhere that experiences shower activity during the peak of this cold air is susceptible for some snow, but likely not accumulating for non-mountainous regions.

The system arriving Wednesday will be rather strong, and feature strong winds in the afternoon and into late Wednesday night. As such, Blizzard Warnings have been posted for the Cascades and Olympics for winds frequently gusting to around 40 to 45 mph as well as visibility reductions down to a quarter of a mile. The Cascade passes will be primarily impacted by these winds, but the Olympics and routes to Hurricane Ridge will also be impacted by blowing snow and strong winds. For travel conditions across the passes, please refer to WSDOT for the latest.

LONG TERM /THURSDAY THROUGH MONDAY/

A number of winter weather headlines will persist into the later half of the week as additional rounds of heavy snow are expected in the mountains. Wednesday through Friday morning storm total snow amounts suggest 2-4 feet across Stevens and Snoqualmie pass, but higher amounts at higher elevations are possible and could reach up to 5 feet of new snow. This is welcome news for the state of the snowpack and snow water equivalent values that have been abysmally low thus far this winter. While not likely to fully rebound conditions to a normal value, it is still of benefit.

Atmospheric river activity will also lend itself to higher QPF amounts in lowland locations, generally areas from Seattle southward to the Chehalis Valley are forecast to receive the most QPF at this time. These locations are also included in Excessive Rainfall Outlooks from the Weather Prediction Center in the midweek time frame as well. Winter storm watches persist into the later half of the week and may be upgraded depending on the forecast over the next several days.

Rain and periods of mountain snow look to continue into early next week.

21

AVIATION

Westerly, zonal, flow aloft over western WA tonight and Tuesday. At the surface, winds largely favoring a SWerly direction. Some obs have already seen a transition to more light and variable, while for all terminals it appears gusts have dropped off a little sooner than expected and speeds are starting to ease. Disturbances aloft will maintain scattered showers, especially along the coast. Most terminals seeing VFR conditions however locations along the east side of the Sound /SEA, BFI and PAE/ currently seeing MVFR conditions as showers pass through. Will continue to evaluate for 06Z issuance, but expectation is for recovery to low-end VFR conditions for these terminals tonight and overnight. 18/33

KSEA...Showers in the vicinity through around 06z tonight. S/SW winds 10-15 kts this evening, although the chance for gusts seems to have dropped off. Diminishing PSCZ should remain north of the terminal, however some VCSH cannot be ruled out. Also in regards to this feature, looks like northerly winds should not impact the terminal, although the convergence may allow for speeds to diminish a little ahead of schedule if the CZ sinks any further south. As noted in main discussion, brief MVFR cigs this evening before recovering to VFR tonight. Possible MVFR may appear briefly early Tuesday morning, but confidence is low. Showers increase by 21z Tuesday afternoon. 18/33

MARINE

Onshore flow will ease tonight. Seas will remain elevated through Wednesday. A strong Pacific frontal system will impact the region on Wednesday with potential for gales over the waters. A weaker system will stall over the region Thursday and Friday. The flow will turn northerly on Saturday, then offshore on Sunday as a warm front moves into southern B.C. 33

HYDROLOGY

Moderate to heavy rainfall over the Olympics will force rises on the Skokomish River in Mason County with flooding possible. The river will remain high through the end of the week. Flooding is also possible on the Chehalis basin rivers including the Chehalis, Newaukum River and Skookumchuck River near Bucoda. Crests on these river will occur late in the week. Several other rivers are forecast to reach Action Stage this week but not flooding. An AR next week is primarily focused north into B.C. but will need watching for any southern tracks into WA.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Storm Warning until 5 AM PDT Tuesday for Cascades of Snohomish and Northern King Counties-Cascades of Whatcom and Skagit Counties.

Winter Weather Advisory from 5 AM to 5 PM PDT Tuesday for Cascades of Snohomish and Northern King Counties-Cascades of Whatcom and Skagit Counties.

Blizzard Warning from 5 PM Tuesday to 11 PM PDT Wednesday 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.

Winter Storm Watch from Wednesday evening through Friday morning 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.

Winter Weather Advisory until 5 PM PDT Tuesday for Cascades of Pierce and Lewis Counties-Cascades of Southern King County.

Winter Weather Advisory until 11 AM PDT Tuesday for Foothills and Valleys of Snohomish and Northern King Counties-Lake Crescent Area Including US 101-Western Strait of Juan de Fuca.

Flood Watch from Wednesday afternoon through Thursday afternoon 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.

PZ...Small Craft Advisory until 5 PM PDT Tuesday for Grays Harbor Bar.

Small Craft Advisory until 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 2 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.

Gale Watch from Wednesday afternoon through Wednesday 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.