textproduct: Seattle/Tacoma

SYNOPSIS

A very active pattern is underway through the next week with a series of systems bringing rounds of rain, higher elevation snow, and windy conditions through the end of the week and this weekend. A more significant atmospheric river event is on track to reach the area Monday and into early next week for widespread significant rainfall and hydrologic impacts. Coastal flooding due to higher astronomical tides will remain minor into early next week.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

The latest forecast remains on track this evening with no updates. Rain continues to fall across the area this evening. This will taper off a bit into tonight until another wave moves across the area Friday bringing a reinforcing round of rainfall. Amounts will be fairly light across the interior with the heaviest rainfall focused along the coast, the western Olympics, and most notably, the Cascades, where 2-3" will be possible through Saturday afternoon. More details on the hydrologic implications below. Lowering snow levels Friday night into Saturday morning will allow a transition to snow at locations down to 4000 ft. This will allow for a round of significant accumulating snowfall at Stevens Pass, for which a Winter Weather Advisory has been issued. Amounts of around 5 to 10" are currently forecast. Heavy snowfall rates under a convergence zone or in periods of heavy precipitation may create hazardous conditions. Windy conditions may limit visibility at time. On that note, winds will increase Friday into Friday night, with gusts up to around 20 to 30 mph. Precipitation and winds will taper off area- wide Saturday night.

Highs Friday and Saturday in the low to mid 50s with lows in the mid to upper 40s.

Tides will peak Friday along the Pacific coast and Saturday through the interior waters. Minor coastal flooding will be possible along the coast, Strait, and north interior waters in this time frame. Coastal Flood Advisories have been issued as appropriate.

LONG TERM /SUNDAY THROUGH THURSDAY/

The overall long-term forecast remains on track with another wave of relatively lighter precipitation on Sunday before an atmospheric river pattern begins to set up Monday and persist through the rest of the period. During that time, significant rainfall is expected, with 2-4 inches possible in the lowlands and 5-10 inches possible in the mountains. Hydrologic impacts will be significant, but details are listed below. Additionally, periods of increased wind will accompany the system, in particular on Monday. Higher snow levels above 5000-6000 ft will allow for rain through the passes and some snowmelt.

AVIATION

Generally a mix of MVFR/IFR and localized LIFR as showers continue across western Washington this evening with northwesterly flow aloft. Substantial low level moisture will likely keep deteriorated conditions throughout the rest of the evening, along with limited vsbys 3-6SM in rain and drizzle. MVFR/IFR will persist into Friday morning, with lower prone locations (KPWT, KOLM, and even KCLM) likely seeing LIFR conditions. S/SW generally 6 to 8 knots throughout the evening will increase by Friday morning to 10 to 15 knots.

KSEA...LIFR ceilings this evening with periodic rain and fog. Ceilings will fluctuate between IFR and LIFR throughout this evening, although probabilities have been trending more towards IFR. Will continue to see vsbys around 4 to 6 statute miles from light rain and drizzle with IFR to LIFR continuing into the morning Friday. S/SW winds 6 kt or less this evening and overnight will increase to 7 to 12 kt once again by 17z Friday. Gusts up to 20 knots can be possible throughout Friday afternoon.

Mazurkiewicz/15

MARINE

A warm front has moved through the waters today for southerly winds, although they have remained under any criteria. A stronger front will move over the waters into Friday, which will result in increasingly strong westerly winds. Latest guidance has increased since the previous runs, with almost 80-90% of gale gusts over the coastal waters. Therefore, have upgraded the Gale Watch to a Gale Warning over all of the coastal waters. Guidance still suggests a 40 to 50% chance of gale gusts in the inner coastal waters, so have included them as well. A strong westerly push is also expected in the Strait, have also upgraded to a Gale Warning for all entrances of the Strait for Friday evening. Additionally, other interior waters such as the Puget Sound and Hood Canal zones, and the Northern Interior waters will see small craft winds during this time.

Additional systems look to move in over the weekend for some elevated and winds and seas, but look to remain generally on the mild side. A stronger system on Monday into Tuesday look to bring winds back up to possibly gale strength, along with elevated seas.

Combined seas 5 to 7 feet will remain through tonight. Seas will start to build upwards to 10 feet by Friday afternoon, building again to 15 to 17 feet by late Friday evening into Saturday morning.

Mazurkiewicz

HYDROLOGY

A series of wet weather systems will increase the threat of river flooding this weekend, especially into the first half of next week. West to northwesterly flow aloft with the first system on Friday will put the area of greatest precipitation in the North Central Washington Cascades. Snow levels, at this time, will be rising over 5500 to 6000 feet.

As the flow aloft becomes more westerly to southwesterly the flood threat will shift to the flood prone Skokomish River late in the weekend.

There's still a wide variance in the possible precipitation amounts with an atmospheric river setting up through the first part of next week, but confidence is increasing in moderate to heavy rainfall across western WA, especially over the Olympics and Cascades.

Confidence is increasing that we will see a widespread river flooding event on our hands beginning late Monday, throughout Tuesday and into Wednesday, with multiple rivers flowing off the Cascades and the Olympics reaching minor and moderate flood stages (potentially nearing even Major flood stage).

Uncertainty still continues to remain in regards to the exact flood levels and stages through next week, and as such it will be critical to monitor the forecasts through the next seven days.

The series of wet systems will start to elevate the landslide risk throughout the weekend, increasing rapidly early next week with the arrival of an atmospheric river.

Mazurkiewicz

SEW WATCHES/WARNINGS/ADVISORIES

WA...Coastal Flood Advisory from 4 AM to 10 AM PST Saturday for Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-San Juan County.

Winter Weather Advisory from 7 PM Friday to 10 PM PST Saturday for Cascades of Snohomish and Northern King Counties.

Coastal Flood Advisory from 9 AM to 3 PM PST Friday for Eastern Strait of Juan de Fuca-Grays Harbor County Coast- Northern Washington Coast-Western Strait of Juan de Fuca.

Coastal Flood Advisory from 9 AM to 3 PM PST Saturday for Grays Harbor County Coast.

PZ...Gale Warning from 1 PM Friday to 4 AM PST Saturday for West Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning from 1 PM Friday to 7 AM PST Saturday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 1 PM Friday to 10 AM PST Saturday for Northern Inland Waters Including The San Juan Islands.

Small Craft Advisory from 1 PM Friday to 4 AM PST Saturday for Puget Sound and Hood Canal.

Gale Warning from 10 AM Friday to 4 AM PST Saturday 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.