textproduct: Seattle/Tacoma

SYNOPSIS

A passing front will bring widespread rain and mountain snow through the day today, with showers lingering through early Tuesday. A brief break in the pattern as transient high pressure moves through midweek, but the next disturbance arrives by Friday. This will maintain rain and mountain snow, along with cooler conditions, though the weekend.

SHORT TERM /TODAY THROUGH WEDNESDAY/

The next front is pushing onshore early this morning, with the associated band of precipitation reaching the coastline at this hour. As this pushes inland, expect to see colder air also filter in the region, bringing the snow level down to around 3000 ft by later morning. Widespread showers continue in the cool, unstable post-frontal air mass, which brings a few inches of snow down to Stevens and Snoqualmie passes through the day. Most likely amounts are short of advisory thresholds, but motorists traveling over the Cascades should expect to encounter winter conditions. There's also a low (around 10-15%) chance of an isolated lightning strike or two near the coast or offshore through the day as lapse rates steepen behind the front.

Showers taper through the morning Tuesday as the upper level support for continued precipitation moves out of the area. This brings a brief intermission to the more active weather as heights rise and we dry out. The other side to this is that cooler overnight temperatures (many spots in the lower 30s) and clearing will give way to another round of morning fog on Wednesday.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Ensemble guidance remains in strong agreement that the brief break will indeed not last long, as the next disturbance will already be approaching by late Thursday. This will bring another round of precipitation chances, but with fairly good agreement in the ensembles that the system will be focused well to our south, this looks to preclude widespread impacts but just a passing focus for additional precipitation (in the form of lowland rain and mountain snow). Nearly all of the ensemble members favor a deeper trough by the end of the weekend that suggest a very high (>80%) likelihood of a colder and wet pattern taking shape late in the weekend.

AVIATION

A bit of a mixed bag of ceilings with MVFR along the coast and northern interior with VFR cigs elsewhere. This is due to scattered showers associated with a front that is beginning to slowly come onshore. Southerly winds of around 7-12 kt is prevailing across the area as well. These conditions will persist into the late morning hours until, behind the front, ceilings lift and scatter and winds begin to ease. VFR conditions will remain across the area through early tonight. Light winds and clearing skies, however, will increase the chances for patchy fog to develop across the area early Tuesday morning.

KSEA...VFR cigs early this morning, but periods of MVFR will be possible through around 18-20Z this morning as a front with scattered showers moves across the area. Ceilings lift and scatter following for a return to VFR conditions. Fog potential will increase going into early Tuesday morning (25-35%). South winds 7 to 10 kt will ease this evening following the frontal passage, becoming light E/SE overnight.

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MARINE

A weak frontal system traversing the area waters today will slightly increase southerly winds across the area today, but this will remain well below headlines. Seas will also remain in the 8-10 ft range. Broad high pressure will set up across the area on Tuesday, allowing winds to remain relatively light and seas to east to around 5-7 ft. The next frontal system will arrive Thursday into Friday, and with it bring a round of increased winds that may require headlines, as well as seas quickly increasing above 10 ft, perhaps over 15 ft by Thursday night. Additional systems through the weekend will keep winds breezy and seas above 10 ft through then.

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HYDROLOGY

River flooding is not expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 4 PM PST this afternoon 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.