textproduct: Seattle/Tacoma

SYNOPSIS

River flooding continues across areas of western Washington. A weak front crosses the region early today. A stronger system will follow Monday into Tuesday, bringing heavier precipitation and strong winds for much of the region areas. A deeper trough will bring cooler air and the potential for heavy mountain snow Tuesday night into Wednesday. Conditions remain unsettled heading into late week with additional rain and mountain snow expected.

SHORT TERM /TODAY THROUGH WEDNESDAY/

A weak front crossing the area this morning is bringing some increase in rain and cloud cover across the area. Rain will move inland by early Sunday, but expect overall amounts to remain rather light, with most areas only expected to receive a few hundredths to a tenth of an inch across the interior and a few tenths along the coast. Snow levels will remain rather high (generally between 6000-8000 ft), so rainfall amounts in the mountains are generally expected to range from a quarter of an inch to an inch in spots, but are not expected to bring additional impacts at this time.

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 through Monday and into early Tuesday 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 - see the hydrology section for additional details.

While the strongest winds will likely in the favored locations along the coast and in the far northwest interior, confidence continues to increase in the potential for 40-45 mph gusts across a large swath of the region with this system. Ensemble guidance suggests a high probability (>80% for 30-40 mph gusts and still about a 60-70% chance for 45+ mph in the favored locales) of seeing winds reach close to, if not exceeding thresholds, and especially given the very saturated conditions across the region, have proactively issued a wind advisory for the lowlands to cover tonight through Monday.

Additional moisture on the backside of the atmospheric river continues into Tuesday, with another front crossing the region later Tuesday into Wednesday. This could bring additional rainfall to the lower elevations, but a cooler air mass arrives with this, with snow levels likely dipping down to around 3000-4000 ft and bringing significant snow to the mountains Tuesday night into Wednesday.

One additional concern for the short term time period will be the potential for high surf along the Pacific coastline at times this week. While seas near the coastline should begin to increase into the 16 to 19 ft range, the dominant periods look to be short enough to limit the overall energy and keep things just shy of criteria. Nevertheless, this will be something else to closely monitor in the days ahead.

LONG TERM /THURSDAY THROUGH SATURDAY/

The pattern stays active and rather damp through much of the week ahead, but with lower snow levels that will bring a more typical pattern of mountain snow and lowland rain through the remainder of the week. Temperatures likely trend cooler during the late stages of this week with daytime highs largely only topping out in the mid to upper 40s and overnight lows trending into the 30s from Thursday onward. Clusters in ensemble members begin to diverge a bit more toward the later week, but all maintain a fairly active pattern. 12

AVIATION

Weak front moving inland today and dissipating. Warm front north of the area tonight with another front moving inland Monday. Southerly flow in the lower levels increasing overnight into Monday morning.

VFR ceilings this morning with the exception of the coast with IFR ceilings. Areas of MVFR ceilings over the interior 17z-22z as the front dissipates over the interior. VFR ceilings this evening lowering to MVFR overnight. Southerly winds picking up overnight with 15 to 25 knot winds with higher gusts after 12z Monday.

KSEA...VFR ceilings. Chance could see MVFR ceilings at times late morning/early afternoon. Ceilings lowering overnight to MVFR by 12z Monday. Southerly winds 4 to 8 knots increasing to 10 to 15 knots with gusts to 25 knots around 12z Monday. Felton

MARINE

A weak front crossing the waters will bring advisory strength winds to the coastal waters and building seas today. A stronger front late Sunday through Monday will bring even stronger winds. The gale warning for the coastal waters has been expanded to included the west entrance Strait of Juan de Fuca, as well as the corridor extending from Puget Sound/Hood Canal north through the northern Salish Sea. Ensemble forecast guidance continues to suggest a 60-70% chance of a period of gale force southerly gusts through these areas. In addition to the winds, expect seas to build to 18-20 ft early in the week and to remain elevated through the week ahead as the pattern remains active.

HYDROLOGY

Most rivers will continue to recede through tonight. Atmospheric river arriving Monday morning with rivers rising again by late morning. Even with the rises most of the rivers staying below flood stage Monday. Rivers going over flood stage will be the ones that will have not dropped below much below flood stage over the weekend like the Skagit, Cedar, White and Cowlitz below Mayfield Dam.

Rain easing Monday night into Tuesday before the tail end of the atmospheric river reaches the area later Tuesday into Wednesday increasing precipitation rates. This second round of precipitation will drive some rivers above flood stage with major flooding possible along the Skagit and lower reaches of the Snoqualmie.

Cooler air moving into the area Tuesday night adds some uncertainty to the river levels. Current forecasts have snow levels dropping to 2000 to 2500 feet by Wednesday morning. There is more moisture with this second surge of the atmospheric river but the cooler air will keep some of the moisture in the mountains in the form of snow. This combination makes for tricky river forecasting.

A flood watch is in effect from Monday morning through Thursday afternoon across the lowlands. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 10 PM this evening to 10 PM PST Monday for City of Seattle-Downtown Everett / Marysville Area- Eastern Kitsap County-Eastside-Foothills of the Western and Southern Olympic Peninsula-Grays Harbor County Coast- Island County-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-Middle Chehalis River Valley-Northern Hood Canal-Northern Washington Coast-Olympia and Southern Puget Sound-Port Townsend Area-San Juan County-Shoreline / Lynnwood / South Everett Area-Southern Hood Canal- Western Strait of Juan de Fuca-Willapa and Black Hills.

Flood Watch from Monday morning through Thursday 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-City of Seattle-Downtown Everett / Marysville Area-Eastern Kitsap County-Eastern Strait of Juan de Fuca-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-Foothills and Valleys of the North Cascades- Foothills of the Western and Southern Olympic Peninsula- Grays Harbor County Coast-Lake Crescent Area Including US 101-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-Middle Chehalis River Valley-Northern Hood Canal-Northern Washington Coast-Olympia and Southern Puget Sound-Olympics-Port Townsend Area-Shoreline / Lynnwood / South Everett Area-Southern Hood Canal-Western Strait of Juan de Fuca-Willapa and Black Hills.

PZ...Gale Warning from 10 PM this evening to 4 PM PST Monday for Admiralty Inlet-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-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 10 PM PST this 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.