textproduct: Seattle/Tacoma

SYNOPSIS

Additional weather systems are forecast to move across the area through the end of the week. Lowland rain, mountain snow and periods of breezy winds can be expected through the weekend. Higher mountain snow amounts are possible early next week with lower snow levels.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

We're in post-frontal onshore flow today with a strong westerly push expected through the Strait of Juan de Fuca. Showers are mostly over the interior and Cascades with a PSCZ starting to form over Snohomish and King counties. Main impact will be lowering snow levels with periods of heavy snow in the Cascades affecting Stevens Pass. Snow shows will also affect White Pass and Paradise on Mount Rainer too. The air mass is slightly unstable with a slight chance of thunderstorms, primarily with the PSCZ band this afternoon and evening. No strikes so far. Showers will mostly linger in the Cascades overnight then taper down Thursday morning as onshore flow eases.

High pressure forms offshore Thursday and Friday with light warm frontal precipitation reaching the area on Friday. Snow levels will be rising (over 5,000 ft) with just a few inches on the higher mountain peaks. Temperatures will track close to average. 33

LONG TERM /SATURDAY THROUGH WEDNESDAY/

The flow aloft will turn westerly this weekend with a frontal system stalled over the region. Snow levels will fall below pass levels on Sunday with winter weather impacts possible at both Stevens and Snoqualmie Pass. We remain cool and wet moving toward midweek with the potential for heavy mountain snow. A rain/snow mix is indicated in the lowlands too due to low snow levels. However, with onshore flow, most impacts (if any) would occur closer to the west slopes of the mountains. 33

AVIATION

Westerly flow aloft continues behind a frontal passage with conditions generally MVFR to IFR this evening as precipitation tapers off. Terminals will see varied VFR to IFR conditions as shower activity decreases overnight into Thursday, confining to the Cascades. Probability is greatest for MVFR ceilings most of Thursday regionwide. Winds will continue to ease overnight and increase Thurs afternoon with gusts to 25 kt generally south and east of the Puget Sound.

KSEA...MVFR conditions this evening as convergence zone shower activity continues to taper off. IFR conditions possible at times, but should stay predominantly MVFR overnight. Winds generally SE 5 to 10 kt overnight. South to west winds increasing Thurs afternoon with gusts to 25 kt possible.

HPR/15

MARINE

A trough/cold frontal system continues to move through the waters this afternoon. Onshore flow has increased already along the coast this afternoon, and will work its way through the Strait of Juan de Fuca tonight/Thursday. A local upgrade of a small craft advisory to a gale warning was issued this afternoon for the central/east Strait of Juan de Fuca (due to HREF/REFS giving a high likelihood of frequent gusts of 35 kt). The small craft advisory was also expanded to include Admiralty Inlet through Thursday afternoon. The coastal waters will see winds decrease early Thursday morning, with the threat transitioning to seas as waves building up to 9-11 ft Thursday. The flow will remain onshore through the remainder of the forecast, with the potential for hazardous winds for small crafts Sunday/Monday, and midweek next week. Seas drop to 5-7 ft Friday through Saturday, then increase to 9-12 ft Sunday through Tuesday before decreasing to 7-9 ft Tuesday through Wednesday.

HPR

HYDROLOGY

No river flooding is expected over the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 10 AM PST Thursday for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County.

PZ...Small Craft Advisory until 10 AM PST Thursday for Admiralty Inlet-West Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning until 10 AM PST Thursday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 1 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.