textproduct: Seattle/Tacoma

SYNOPSIS

Significant river flooding continues across many areas of western Washington. Drier conditions develop today, but a weak front crosses the region by early Sunday. A stronger system will follow Monday into Tuesday with heavier precipitation and potentially strong winds for some areas. A deeper trough will bring a cooler air and the potential for heavy mountain snow Tuesday and Wednesday.

SHORT TERM /TODAY THROUGH SUNDAY/

High pressure building over the region maintaining a stable air mass with light winds, along with drier conditions. Numerous rivers remain above flood stage and resulting impacts from river flooding will continue today. Expect some areas of fog to develop early this morning toward daybreak, though a persistent cloud deck may prevent visibilities from becoming significantly restricted. The ridge flattens out into Sunday with a weak system sliding across the area. This will reinforce the cloud cover and bring some light precipitation to portions of the area. Snow levels remain high, but amounts are light enough to not bring much in the way of impacts or concern. 12

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

A different story emerges Sunday night into Monday, when the next atmospheric river taking aim at the region. Snow levels will remain rather high at the onset (above 7500 ft), and rainfall amounts look be be on the order of around an inch for the lowlands and 2-4 inches in the mountains through late Monday, with the mountain amounts highest in the Cascades from around King County northward. This would have the potential to bring prolonged or renewed flooding on many areas rivers. Gusty winds also are likely to increase with this frontal system with gusts reaching 30-40 mph remaining likely (>60% chance) through the coastal and favored windy locations in the interior. The pattern stays active and rather damp through much of the week ahead, but the arriving trough will bring snow levels dipping down to below the Cascade passes through the day Tuesday and to around 2500 ft Wednesday. This will set the stage for potential heavy snowfall in the mountains during the midweek time period. Meanwhile, this will bring additional rainfall to the lowlands through much of the week ahead with a moist and active weather pattern remaining in place. 12

AVIATION

Upper level ridge over Western Washington with the ridge axis moving east of the area later this morning. Westerly flow aloft becoming southwesterly late morning. Light flow in the lower levels.

Real mixed bag out there this morning. Stratus deck between 3000 and 6000 feet preventing the scattered cloud deck below 1000 feet from becoming ceilings. With the light flow will go for ceilings lowering down to IFR 14z-16z. Ceilings improving in the afternoon with just middle and high level clouds by 01z. Cloud deck around 5000 feet developing overnight with the upper level ridge continuing to move east and a weakening front approaching the coast.

KSEA...Ceilings near 4000 feet lowering to below 1000 feet around 15z. Could see some visibility restrictions down to as low as 3 sm. Ceilings lifting this afternoon with VFR ceilings by 01z. Light south southeast wind 6 knots or less. Felton

MARINE

A weak front will cross the waters later today through early Sunday, with advisory strength winds expected over the coastal waters. A stronger system arrives Sunday night into Monday and is more likely to bring widespread advisory winds to all waters and some potential (40-50%) for gales over the coastal waters. Seas will increase with these stronger winds late Sunday/Monday, and with the arrival of larger swell at the same time, expect to see 15-20 ft seas across the coastal waters early in the week. Yet another disturbance in the Pacific parade of weather systems will bring a reinforcing round of winds and again building seas around midweek. 12

HYDROLOGY

Rivers continue to recede this morning as Western Washington gets a break from the wet weather. Even the lower reaches of the rivers will approach or lower below flood stage later today into tonight. The exception to this will be the lower reaches of the Chehalis river which will not fall below flood stage until Sunday from Porter down to Grays Harbor and the lower reaches of the Skagit river which will recede to near flood stage by Monday morning.

Rivers will be on the rise again later Monday into Tuesday with another atmospheric river taking aim at Western Washington. Rainfall amounts to 3 to 5 inches Monday through Wednesday in the mountains are forecast. Another round of river flooding will occur with the atmospheric river but at this time none of the forecasts have any major flooding on the rivers ( the Skagit at Mount Vernon gets close Tuesday night and the Snoqualmie at Carnation gets close Wednesday ).

With very wet antecedent soil conditions, the landslide threat remains high across the region. Potential is also elevated for debris flows over area burn scars, which continue to be monitored.

The threat of urban flooding will increase again later Monday into Tuesday. Small stream flooding, as well as areas with poor drainage, will pose a risk of localized nuisance flooding and ponding on roadways later Monday into Wednesday. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 4 PM this afternoon to 1 PM PST Sunday 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.