textproduct: Seattle/Tacoma

SYNOPSIS

Cool, wet and windy conditions Tuesday into Wednesday with periods of heavy snow in the mountains. Drier weather is in store Thursday and Friday with high pressure. Wetter weather returns over the weekend.

SHORT TERM /TODAY THROUGH THURSDAY/

Wet and windy conditions on tap today as a strong Pacific storm system sweeps through western WA. The main impact will be periods of heavy mountain snow, including snow at all Cascade passes - Winter Storm Warnings are in effect. Snow levels will hover around 3500 ft today but will drop to 1500-2000 tonight into Wednesday. The bulk of the heavy snow will fall tonight but there will be lingering snow showers moving through Wednesday. Mean 48-hr storm total amounts range from 10 to 20" with highest amounts over the volcanoes. Heavy snow is also possible for the Olympics and a Winter Weather Advisory is also in effect (primarily for today and tonight). In addition, it'll be windy today with gusts to 20-30 mph common across most lowland areas. Winds will peak this evening but still remain in 15-25 mph range overnight.

A deep upper low will be overhead on Wednesday with cool and showery conditions. As mentioned above, we'll still see snow showers in the mountains although snow rates will ease. The air mass is slightly unstable with a chance of thunderstorms too, especially near the coast. Showers will taper off Wednesday night as the low opens to a trough and exits east. It's not as windy but will be chilly with morning lows in the 30s and highs in the 40s to around 50.

We're under dry northerly flow on Thursday as high pressure forms offshore. Morning temperatures will remain cool and in the 30s with freezing temps and frost possible across the south sound. Highs will be a little warmer and in the 50s with sunbreaks. 33

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

High pressure will shift inland on Friday for more dry and stable weather. Morning lows will still track on the cool-side with possible frost around the south sound. The ridge departs on Saturday with a return of moist SW flow. Showers associated with an offshore low may clip the coast during the afternoon and evening. Showers will spread inland on Sunday as the low shifts farther east and inland. By Monday, this system shifts to our south, over CA/NV, with a brief break in the weather over western WA. 33

AVIATION

A shortwave trough/cold front will swing through the terminals today. Flow aloft will remain westerly with a jet core moving ashore and southward through the day. Showers in the north interior/coast this morning will become widespread and a steady rain later in the day (snow in the mountains above 3,500 ft). There is a 15-20% chance of thunder in the afternoon/evening for coastal terminals, and the north interior (especially with a post-front convergence zone likely to produce localized heavier rain around/east of KPAE). Precipitation post-front wraps up around 10Z. Wednesday's system will produce scattered showers under an unstable airmass/trough (thunder threat is more widespread across the terminals at 20-25%). Ceilings: MVFR ceilings increase in coverage through the morning, with higher likelihood of IFR conditions in mountain/coastal areas in the afternoon/evening, as well as in heavier rain. Visibilities will decrease this afternoon with rain down to 3-5 SM (less than 3 SM along the coast), with localized drops likely in heavier showers. Southwest winds 8-12 kt gusting to 20 kt increase to 10-20 kt gusting to 30 kt from 15Z Tuesday - 06Z Wednesday, then becoming light.

KSEA...Showers arriving this morning, becoming a more steady rain later this afternoon/evening. Possible convergence zone to the north of the terminal (around KPAE). MVFR ceilings this morning likely to continue through late tonight/Wednesday before improving to VFR. Visibility drops down to 3-5 SM likely with the steadier precipitation this afternoon/evening. Southwest winds 8-12 kt gusting to 20 kt increases to 10-20 kt gusting to 30 kt from 15-18Z Tuesday through 06Z Wednesday. Thunder threat over the terminal today is less than 10%, but increases to 20-25% Wednesday, with the coverage being more scattered.

HPR

MARINE

A trough/cold front will cut over the waters today with widespread showers/steady rain. There is a 20% chance of thunder for the inner coastal waters, and the north interior waters. Winds have begun to pick up out of the southwest this morning ahead of the front. This will peak in the interior waters late this morning/tonight with winds of 20-30 kt. The coastal waters/Strait of Juan de Fuca will see the strongest winds around the same time from the west, and at around the same magnitude (20-30 kt). Small craft advisories remain in effect in these areas with the frontal passage. The winds decrease Wednesday, although the pattern will remain unsettled with a cool trough producing scattered showers and a 20-25% chance of thunder across all waters. Conditions dry out Thursday through next weekend, with another system Sunday potentially producing gusty winds in the coastal waters.

Seas increase from 4-6 ft to 9-12 ft Tuesday, lingering at 8-10 ft through Thursday, then decreasing to 3-5 ft Friday through SUnday before building back to 8-10 ft.

HPR

HYDROLOGY

No river flooding the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Storm Warning from 11 AM this morning 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.

Winter Weather Advisory until 11 PM PDT this evening for Olympics.

PZ...Small Craft Advisory until 2 AM PDT Wednesday 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 from 9 AM this morning to 2 AM PDT Wednesday for Admiralty Inlet-Northern Inland Waters Including The San Juan Islands.

Small Craft Advisory from 6 AM this morning to 2 AM PDT Wednesday for Puget Sound and Hood Canal.

Small Craft Advisory from 5 AM early this morning to 5 AM PDT 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.