textproduct: Seattle/Tacoma

SYNOPSIS

Periods of lowland rain, mountain snow, and gusty conditions will continue through the first part of the week as a series of weather systems moves across the region. A few weaker systems look to move up into the area mid to late week, but expect an overall trend towards cooler and drier conditions.

SHORT TERM /TODAY THROUGH TUESDAY/

A broad upper level low over the Gulf of Alaska will continue to eject shortwaves into the region through the near term. Meanwhile, at the surface, the next weakening frontal system will move across western Washington today, bringing the next round of lowland rain and mountain snow to the area. Showers will increase in coverage through the morning and afternoon hours as the system makes its way into western Washington. Overall rainfall amounts will range from 0.25-1.00 inches across the lowlands, while a few spots like Port Townsend, Sequim, and Whidbey Island will likely see lower amounts due to rain shadowing. Additional rounds of snow are likely for the mountains, with snow levels generally hovering between 2500-3500 ft this morning and falling to 2000-2500 ft by tonight. Highest snow totals with this system will be across the far northern Cascades of Whatcom and Skagit counties- where Winter Storm Warnings are in effect for an additional 1 to 2 feet of snow. Snow amounts across the Central Cascades will be lower and are generally expected to be between 6-12 inches, with Stevens and Snoqualmie passes likely only seeing around 4-6 inches, while White Pass will see slightly higher amounts between 7-9 inches. Southerly winds will become breezy again today, picking up through the morning hours and gusting to 30-35 mph. Winds will remain elevated through this afternoon, before easing again this evening.

A more organized system will move into the area on Monday, bringing steadier rainfall to the lowlands, additional rounds of mountain snow, and another round of gusty winds to western Washington. Rainfall amounts will generally be between 0.25-0.50 inches across the interior lowlands and between 0.75-1.00 inches along the coast. Snow levels will hover between 2500-3000 ft for additional rounds of snow across the Olympics and Cascades. Southerly winds will pick up again during the early morning hours on Monday. The strongest winds will be along the coast and for areas north of Everett, where gusts between 45-50 mph will be possible at times. Elsewhere, wind gusts to 40 mph will be possible through the day, before winds gradually start to decrease again on Tuesday night.

Lingering precipitation will then taper through the day on Tuesday. At this time, Tuesday looks to bring a quick little break in between systems.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Ensembles remain in pretty good agreement with the upper level trough digging across the northeastern Pacific and swinging additional disturbances across western Washington through the long term. While overall conditions are trending drier as a whole for the second half of the week, additional rounds of lowland rain and mountain snow will be possible at times through the period. The weather pattern also continues to favor 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. Should precipitation overlap with the cooler temperatures, could even see a few spots of rain/snow mix across the lowlands, though confidence in this remains low at this time.

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AVIATION

Persistent troughing over the eastern Pacific will keep west-southwesterly flow aloft over W WA before shifting more definitively southwesterly this evening. Surface winds will ease a little this early morning down to 4-8 kts for many terminals before seeing speeds return to generally 8-12 kts with more wind prone terminals such as HQM potentially seeing some gusts up to 25 starting this afternoon through the remainder of the TAF period.

Cigs over W WA this morning are of two camps: locations seeing showers falling under MVFR conditions while locations outside of the primary band of showers, generally from PAE south, are VFR. Models are showing varying degrees of skill in capturing this, which poses forecast problems. May need to do a little tweaking with the 12Z issuance, keeping MVFR conditions in locations that are already seeing them due to aforementioned showers while keeping remaining areas VFR. As more organized precip is expected to move into the area late this afternoon through the rest of the TAF period, that is likely when widespread MVFR to IFR conditions will return and linger into early Monday morning.

KSEA...VFR conditions in place with majority of showers moving north of the terminal. Sea-Tac does seem to be just on the southern edge of things, so the VCSH in the TAF looks spot on. Cigs might be a little on the pessimistic side as latest data suggests that the return to showers and MVFR conditions may hold off until 00Z or a little later. Beyond that, forecast is on track. Winds generally 5- 10 kts and should remain that way for much of the generally dry period mentioned above. As lower cigs and precip move in, so too will the stronger winds with speeds increasing to generally 8-12 kts.

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MARINE

Winds have eased a little bit ahead of schedule this early morning and as such the inherited SCA has been cancelled as both winds and seas are now below criteria. A stronger Pacific storm system is slated for Monday which may bring gales to the coastal waters and heightened wind speeds for interior waters as well. Inherited Gale Watch for the coastal waters looks good...although will advise incoming shift that a lead-up SCA for late tonight may not be a bad idea. Winds over the interior waters showing borderline SCA conditions but confidence is not quite there yet...thus no headline with the morning forecast. Low pressure will weakens offshore Tuesday allowing for offshore flow Wednesday. This offshore flow will strengthen on Thursday due to high pressure over interior B.C. and low pressure off OR/CA coast. 18/33

HYDROLOGY

Although showers are expected over W WA today and Monday, precip amounts should not interfere with the overall downward trend being seen on most area rivers. Rivers with dam regulated flows expected to remain below flood levels at this time, however the decisions behind releases and managing river levels is a day by day thing. As such, those living near these rivers should remain mindful of latest river forecasts as flows may increase from time to time 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.

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

The more showery nature of precipitation over the past couple of days has limited the landslide threat, however the incoming system for Monday appears to be more organized. This may bring a return to a heightened threat for landslides.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Coastal Flood Advisory from 5 AM to 11 AM PST this morning for San Juan County.

Winter Storm Warning until 4 AM PST Monday for Cascades of Whatcom and Skagit Counties.

Winter Weather Advisory until 4 AM PST Monday for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County.

PZ...Small Craft Advisory until 4 PM PST this afternoon 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.

Small Craft Advisory until 1 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.

Gale Watch from Monday morning through Monday evening 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.