textproduct: Seattle/Tacoma

SYNOPSIS

Drier weather on Friday with transient ridging across the region. The pattern will amplify again over the weekend as an upper-low digs over the offshore waters from the Gulf of Alaska. Several rounds of lowland rain, mountain snow and gusty winds are favored into next week.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

A shortwave is traversing across the region this evening, leading to scattered shower activity across areas of terrain such as the Cascades and Olympics including Lake Cushman/Hood Canal. Some snow has been observed over these areas but significant accumulation is not expected. For tonight, conditions are slated to dry out as a transient ridge builds in out of the northwest. Fraser Outflow will persist but weaken tonight over the northern inland interior. Nonetheless, a Cold Weather Advisory has been issued for western Whatcom county for tonight. Wind chill values between 15-20 F are expected. Overnight lows are to bottom out between the lower to upper 20s.

Ridging will not only bring dry weather but relatively warmer conditions on Friday with highs in the lower 40s. Temperatures will remain below seasonal averages but it'll be the start of a warming trend leading into the weekend. Pattern progression in the upper-levels on Saturday as models have the aforementioned ridge axis east of western WA, over the Inland Northwest. Deterministic and ensemble guidance are in lock-step, showing an upper-low digging southward from the Gulf of Alaska and sitting over the offshore waters of the US West Coast. This feature will swing shortwaves into the PNW, allowing the return of widespread lowland rainfall, mountain snow, and even breezy to gusty winds along the coast and Cascade gaps on Saturday.

LONG TERM /SUNDAY THROUGH THURSDAY/

Most ensembles keep the low offshore Sunday and into Monday, with multiple rounds of precipitation via shortwaves continuing during this time. Highs will remain in the lower 50s through the long- term, right around seasonal average for late February. The moisture content of the precipitation will increase on Monday and Wednesday. Hydrologic flooding impacts are not expected, but there remains potential for mountain snow with this system. There is lower confidence in heavier snowfall rates, as well as snow levels with the warmer air in place, but large-scale impacts are not expected with the snow being spread across several days (Wednesday is the only day where the snow may be heavy enough to produce possible travel impacts).

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AVIATION

Northwesterly flow aloft across the region with an upper low dropping south into California and Nevada offshore. A few wraparound showers near the Olympics this afternoon, but otherwise cloud cover continues to decrease. This has mostly VFR conditions under broken to scattered mid clouds. Breezy Fraser outflow winds continue to impact KBLI but continue to weaken today. Lower ceilings again develop across the south overnight, but northerly flow will aid in drying and could keep ceilings closer to 3000 ft or higher overnight across much of the area. Mostly VFR conditions again Friday with increasing mid clouds ahead of the next disturbance.

KSEA...VFR conditions with shower activity shifting south. Surface winds northerly at around 10 kt through the day, veering to southeast and easing this evening through the night. This brings the potential of low VFR to MVFR ceiling (around a 25-30% chance) after 12z Friday through mid morning. Cullen

MARINE

Seas continue to subside a bit today, holding in the 6 to 8 ft range. Some gusts to near 20-25 kt associated with Fraser outflow through this evening too, but these are decreasing and less widespread.

Light offshore flow will then continue into early Friday with a broad surface trough over the coastal waters. A stronger system will move into the area waters over the weekend, increasing offshore flow and likely bringing southeasterly gales to the coastal waters. Latest probabilistic guidance continues to suggest around a 50% chance of seas building into the 18 ft or larger range over the coastal waters this weekend, with a significant southerly contribution. An active pattern remains in place into next week, as gusty winds and larger seas reinforced by each subsequent disturbance through the week ahead. Cullen

HYDROLOGY

No river flooding is expected over the next seven days but later next week chances increase significantly for flooding on the Skokomish River. Starting this weekend through next week there will be multiple rounds of widespread precipitation along with warming temperatures to raise the snow level. With the thin mountain snowpack and existence of low elevation snow, rain on snow could produce enough snow melt getting added to the otherwise unimpressive forecast precipitation amounts to result in flooding.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Cold Weather Advisory from 7 PM this evening to 10 AM PST Friday for Lowlands of Western Whatcom County.

PZ...Gale Watch from late Friday night through late Saturday night 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.