textproduct: Seattle/Tacoma

SYNOPSIS

Periods of lowland rain, mountain snow, and breezy conditions will continue across western Washington over the next week as a series of weather systems moves across the region. A trend towards cooler conditions looks likely around midweek.

SHORT TERM /TODAY THROUGH MONDAY/

A broad upper level trough over the Gulf of Alaska will continue to steer shortwaves across the region through the weekend. This will maintain unsettled and showery conditions across western Washington, with the latest radar showing showers continuing to stream across the area early this morning. Snow will continue for the mountains, with snow levels generally expected to remain between 1500-3000 ft through the weekend. A Winter Storm Warning remains in effect for the Cascades, where roughly another 1-2 ft is expected to fall at Snoqualmie and Stevens passes through this afternoon. Snow will be heavy at times, especially during the late morning and afternoon hours, so use caution if you're planning to travel across the Cascades. In addition to snow, a slight chance of isolated thunderstorms will remain possible for areas primarily along the Pacific Coast both today and again on Sunday. Overall rainfall amounts for the lowlands through Sunday night are still expected to be within 0.50-1.50 inches as a whole, though some areas across the central Sound and northeastern Olympic Peninsula will likely see some lower amounts due to rain shadowing. Southerly winds will be breezy at times through the day Saturday and again on Sunday, with winds generally expected to persist between 25-30 mph.

A stronger system will then move into the area on Monday and will bring another round of gusty winds, lowland rain, and mountain snow to the area. Southerly winds will pick up during the morning hours and will peak in the afternoon at 30-35 mph, before decreasing again by late Monday. Another 9-12 inches of snow will be possible for the mountain passes, with locally higher totals expected for higher elevations. Rainfall amounts of 0.25-1.0 inch are expected for the lowlands.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Conditions look to remain rather active through much of the next week as ensembles remain in pretty good agreement with the upper level trough digging across the northeastern Pacific and swinging additional disturbances into the region. This would continue to bring periods of lowland rain, mountain snow, and breezy winds to western Washington through much of the next week. The weather pattern will also allow for a trend towards cooler temperatures, especially during the overnight period, where we may start to see morning lows approach freezing in some spots by midweek.

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AVIATION

Zonal flow aloft will persist throughout the day today before shifting more southwesterly by Sunday morning. Surface winds over W WA this early morning are south to southwesterly with speeds generally 8-12 kts. PAE stands out as the exception where speeds there are generally 17-22 kts with gusts up to 35 kts. These are expected to ease at least somewhat to better sync up with the speed range at other terminals. For those remaining terminals, speeds will not fluctuate much throughout the day.

Cigs largely MVFR for much of the area, although there are some VFR spots along the coast and along the Strait into the San Juans. PWT, being prone to lower cigs is the sole terminal reporting IFR conditions. With another round of showers expected to move into the area late this morning/early this afternoon, any improvement to cigs will be limited, if existent at all. Latest forecasts suggest that this activity will likely pull cigs a little bit lower with some locations dipping into low-end MVFR. Isolated spots of IFR will still be possible, especially those terminals more prone to lower cigs.

KSEA...MVFR conditions in place with cigs sinking a little bit more around 18Z as the next wave of showers moves into the area. While this will likely result in low-end MVFR conditions /1000-1500 ft cigs/, scattered clouds just beneath that may allow for brief periods of IFR conditions. Models do not seem particularly confident in that and will evaluate whether or not to include in 12Z issuance. Surface winds to remain elevated, generally 8-12 kts...but not so confident in the presence of gusts. They may be isolated in nature, but not sure if they warrant inclusion into the dominant weather features.

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MARINE

Winds will be breezy across portions of the coastal waters, Puget Sound, Admiralty Inlet, and the Northern Inland Waters today, with hi-res probabilities showing roughly a 70-90 percent chance of winds exceeding 21 kt across these spots by late morning. A slight chance of thunderstorms will also remain possible again this afternoon and evening, with the highest chances remaining confined to the Pacific coast and across the Western Strait of Juan de Fuca. Gusty winds, brief heavy downpours, reductions in visibility, and lightning will be possible in any storms that do develop across the waters.

A weakening frontal system will then move into the waters on Sunday, bringing another round of breezy southerly winds to the area. A stronger system is then set to move into the area waters on Monday. Overall, expect an active pattern to continue across the area waters throughout the week, with additional rounds of elevated winds and seas and headlines likely.

Seas continue to hover between 10-12 ft early this morning and will gradually subside towards 8-10 ft by this evening. Seas are expected to rise again by late Monday, approaching 12-14 ft again across the coastal waters.

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HYDROLOGY

Although showers are expected over W WA for much of the day today, precip amounts should not interfere with the overall downward trend being seen on most area rivers. Rivers with dam regulated flows expected to remain near or just over flood levels for the time being as the process of eliminating excess water from previous atmospheric rivers continue.

As for rivers that are still in flood without dam regulation:

* The Chehalis River at Porter will hover near Minor Flood stage for the next few days before receding, while the upstream gauge at Grand Mound has crested below flood stage and will see river levels recede gradually over the next couple of days.

* The Skokomish River at Potlatch also sees river levels gradually easing while remaining in Moderate Flood stage. However, additional rises are expected in the river for the start of next week...keeping the waters in Moderate Flood stage.

* The Cowlitz River at Randle continues to recede gradually, only having fallen below flood stage late last night /11 PM PST Friday/. So it may be okay to drop the warning later this morning. Mayfield Dam is also reporting flows just under flood stage, but with forecast levels hovering right around flood stage, it will be worthwhile to keep this warning up at least in the short term.

With the variances based on needs associated with dams and regulated rivers, flows may increase or decrease below forecast levels rapidly. That said, rivers that remain right around flood stage, even those that linger just below, will likely retain their headlines in case the situation changes.

The latest wave of showers will continue to fall on already saturated ground and as such, the landslide threat will remain high through the weekend.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Storm Warning until 4 PM PST this afternoon 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.

Flood Watch until 10 AM PST this morning for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County- City of Seattle-Eastside-Foothills and Valleys of Central King County-Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Snohomish and Northern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Shoreline / Lynnwood / South Everett Area- Willapa and Black Hills.

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-Grays Harbor Bar.

Small Craft Advisory until 10 AM PST this morning for Central U.S. Waters Strait Of Juan De Fuca-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 7 AM this morning to 4 AM PST Sunday for Admiralty Inlet-Northern Inland Waters Including The San Juan Islands.

Small Craft Advisory until 10 PM PST this evening for Puget Sound and Hood Canal.