textproduct: Seattle/Tacoma

SYNOPSIS

A warm front approaching the coast this afternoon will continue to move across the region tonight into Monday. Warmer air will bring snow levels up, bringing a wintry mix of precipitation to central portions of the Cascades, and rain to the remaining lowlands. Snow levels will continue to rise through the week, warming temperatures at the surface, with wet weather continuing as well through the end of the week.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

The axis of an upper level ridge centered over Washington state this afternoon will slide southeastward tonight into Monday, given the region a west-southwesterly flow with a strong jet streak/atmospheric river aimed at southern British Columbia. A warm front is approaching from the west this afternoon, and will move across the region this evening into Monday. Temperatures have warmed along the coast to where rain will be falling. Further inland, temperatures this afternoon made it into the 40s (and even a couple of 50s). The snow levels are expected to rise tonight into Monday morning as the warm front sweeps through the state. The lowlands will only see rain with precipitation tonight/Monday (and through the week). The precipitation falling in the Cascades this evening is expected to start as snow, and then transition to freezing rain/wintry mix going into early Monday morning. Some of the initial bands that move through the northern Cascades may produce snow rates up to an inch an hour. For this reason, the winter weather advisory was expected for tonight to include Stevens Pass (snow threat), with the potential for up to 6 inches of new snow accumulations. For Snoqualmie Pass, the advisory expansion was primarily for the concern of ice accumulations from freezing rain. The pass will most likely see 0.05-0.10 inches of ice tonight, on top of a wet slushy 2-4 inches of new snow. Anyone traveling through the passes tonight should use caution, and watch for potential slippery spots on roads.

The first round of QPF with the warm front will wrap up Monday evening, with another round expected to arrive on Tuesday. The bulk of the precipitation will fall in the Cascades and the Olympics/Pacific Coast regions. Snow levels will remain high at 8,000-9,000 feet, which will likely cause some runoff from melting snow/wet soils. Please see the hydrology discussion for further details on river flooding potential. Temperatures Monday and Tuesday will be a few degrees warmer, with highs in the mid to upper 50s (a few low 60s are likely in the south interior). A few locations in the north interior/coast will see breezy conditions Monday into Tuesday, with gusts out of the south up to 25-35 miles per hour.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

The models keep the warm and wet pattern going through the week, with the precipitation scaling back on Friday into next weekend. The heaviest of the precipitation remains focused in the Cascades and the Olympics/Pacific Coast, although the amounts in the second half of the week have dropped slightly. Ensembles are showing a cooler trend going into next weekend, with some disagreements into how cool and wet it will be. Nevertheless, the snow levels will drop from 8,000 feet down to around 3,000 feet next weekend, though with highs likely remaining in the 50s, and the overnight temperatures dropping back into the 30s.

HPR

AVIATION

A warm front will clip the area tonight and Monday with westerly flow aloft. Ceilings will decrease to low-end VFR to MVFR range with light rain. The front will lift north into B.C. Monday afternoon for a brief break in rain. Rain returns Monday night as the frontal boundary sags south into western WA, bringing MVFR conditions. 33

KSEA...Light rain and lower cigs tonight with light SE winds. Mainly MVFR conditions moving through Monday. 33

MARINE

Southerly flow will increase over the waters tonight and Monday as a warm front lifts north into B.C. Seas will remain elevated through Tuesday. Southerly flow will prevail through Thursday generally within 10-20 kt range. The flow will then flip to northwest or west on Friday behind a cold front. 33

HYDROLOGY

River flooding continues for the Chehalis River near Grand Mound and at Porter. The rivers will recede tonight and Monday.

Attention then turns to an atmospheric river moving into the region this week. While the bulk of the moisture will initially move into British Columbia, it will gradually sag southward into our area by Tuesday and will bring periods of rain through much of the week. Higher snow levels and rain on recent snows in the mountains could bring additional flooding concerns to portions of the area as several rivers are forecast to rise into Action Stage. For now, the only river forecast to reach flood stage is the Skokomish River- but river forecasts will bear watching over the coming days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory from 5 PM this afternoon to 9 AM PDT Monday for Cascades of Whatcom and Skagit Counties.

Winter Weather Advisory from 5 PM this afternoon to 2 AM PDT Monday for Cascades of Snohomish and Northern King Counties-Cascades of Southern King County.

PZ...Small Craft Advisory until 5 AM PDT Tuesday 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-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 5 AM Monday to 5 AM PDT Tuesday for Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.