textproduct: Seattle/Tacoma

SYNOPSIS

An upper level trough will remain overhead across the northeast Pacific and western Washington through Thursday, before moving inland. Shower activity will continue through Friday, with mixed precipitation remaining a possibility, especially in the early AM hours. Fraser River outflow in the North Interior will result in cold wind chills next few mornings. Temperatures warm up next weekend into next week with a system expected to produce more widespread precipitation, and gusty winds.

SHORT TERM /TODAY THROUGH FRIDAY/

An upper level trough (now nearly stacked over the northeast Pacific off the Washington coast) remains in place this morning, with the center of the low near Neah Bay. This trough will being to move southeastward tonight, before being allowed to move inland Thursday into Friday.

Showers persist across portions of the coast and Snohomish/Skagit counties this morning, but with temperatures above freezing, precipitation type below 500-1000 ft should be mostly rain at this point and will be for the rest of the day.

HREF ensembles show another round of showers moving from the coast inland across the interior later this afternoon/evening. Rain/snow mix is expected with this round of showers, with impacts remaining minimal. Fraser River Outflow is expected to amplify tonight/Thursday morning with increasing northeast winds of up to 15-25 mph pushing down to as far as the Strait of Juan de Fuca. This will likely create wind chill values into the teens and 20s across a larger area across the northwest interior.

As the trough moves inland Thursday/Friday (and is replaced by a brief ridge), the precipitation chances will decrease to just the mountains and the coast Thursday into Friday (but there will remain a slight chance of precip Friday for most areas). There will remain a wind chill/apparent temperature concern for Friday morning from the end of the Fraser River outflow Thursday. A good chunk of the region will likely see some sunshine Friday afternoon (thanks to the ridge), but will continue to see highs in the 40s.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

The ensembles continue to favor another upper level low dropping south from the Gulf of Alaska, to offshore of Washington this weekend into next week. There is some wobbles in the exact placement of the low (and jet funneling in some of the moisture), but it appears that the precipitation will be spread out across the Saturday-Tuesday timeframe (with the bulk of the QPF falling Monday and Tuesday). There was a downward adjustment in the total amount of QPF falling with this system, but the primary impact remains snow in the mountains, with probabilities of 6 or more inches of snow remaining very high early next week. There may also be a period of breezy winds Saturday into Sunday for areas west of the Olympics, with medium probabilities of wind gusts exceeding 30 mph. Additionally, this system is expected to generate large waves offshore the Pacific Coast, that may result in high surf conditions Saturday and Sunday for beaches/coastal areas. Temperatures will warm up into next week, with highs in the lowlands returning into the upper 40s to low 50s. Overnight temperatures will improve into the upper 30s to low 40s.

HPR

AVIATION

West to southwest flow aloft will continue into tonight across Western Washington as a broad upper level trough remains over the Pacific Northwest. The air mass remains quite cool with areas of MVFR or localized IFR in scattered rain and snow showers this morning. A general trend toward improving ceilings is expected this afternoon with VFR most areas, but scattered showers will continue to produced localized MVFR ceilings into this evening. Shower activity will diminish tonight with low level north to northeasterly flow increasing as Fraser River outflow develops across the North Interior. This will act to dry the lower levels somewhat, but redevelopment of IFR or LIFR stratus is expected again late tonight across the Southwest Interior, south Puget Sound and areas in the vicinity of Hood Canal. Local gusty surface northeasterly winds are expected tonight and early Thursday near KBLI.

KSEA...MVFR ceilings with scattered showers in the vicinity are expected to continue through around 19-20Z. Mainly VFR is expected thereafter though ceilings may briefly touch MVFR thresholds with passing showers into this evening. Surface winds southerly 7 knot or less will veer N/NE 7 to 10 knots after around 03Z this evening.

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MARINE

A surface trough over the Washington coastal areas will shift southward tonight into the Oregon waters. A surface ridge will strengthen tonight over the interior of British Columbia for a brief increase in Fraser River outflow and easterly flow near the west entrance to the strait. Light offshore flow will continue into Thursday and Friday with a broad surface trough in place across the coastal and offshore waters and a weak ridge east of the Cascades. Low pressure at the surface and aloft will deepen offshore over the weekend for increasing offshore flow and likely wind related headlines for the coastal waters, strait entrances, and northern inland waters. This pattern will persist into early next week.

Coastal seas will briefly dip below 10 feet today into Thursday, but increased activity offshore this weekend and beyond will drive seas back into hazardous double digits once again as additional large swell trains arrive.

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HYDROLOGY

No river flooding is expected in the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Cold Weather Advisory until 10 AM PST this morning for Lowlands of Western Whatcom County.

PZ...None.