textproduct: Seattle/Tacoma

SYNOPSIS

An atmospheric river will produce periods of moderate to heavy rain from tonight through Monday night. This rain, along with a mild air mass brining snow levels rising above pass level, with bring rises on many area rivers. Flooding is expected on the Skokomish River. Strong high pressure then builds into the region by the middle of the week, bringing a stretch of dry conditions.

SHORT TERM /TODAY THROUGH MONDAY/

High and mid level clouds continue to filter across the region early this morning as a warm front approaches the outer coastal waters. The high clouds and weak low level offshore flow have managed to limit low cloud and fog formation thus far this morning. Rain will shift onshore along the coast ahead of the front this afternoon then spread to interior areas tonight. Periods of moderate to heavy rain will develop by early Sunday with snow levels rising above the passes as the axis of an atmospheric river settles over the northern two thirds of the CWA. Heaviest precip is expected in the Olympics and the north/central Cascades. Sharp rises are expected on the rivers with the Skokomish expected to reach flood stage. More detail can be found in the hydrology discussion section.

Breezy to locally windy conditions will develop later tonight through Sunday, but speeds presently are expected to remain sub-advisory levels. The windiest period looks to be Sunday afternoon into Sunday night...particularly for the North Interior and coastal areas. Wet conditions continue into Monday with the axis of heaviest precipitation expected across the northern half of the forecast area. As is typical with mild atmospheric rivers, temperatures will remain several degrees above seasonal averages.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Upper ridging centered well to our south begins to build northward Monday night into Tuesday which will shove the moisture northward back into British Columbia and begin to allow the area to dry out. Models continue to try to bring a weak front into the area on Wednesday, but dissipate it quickly as it runs into the ridge. It wouldn't be surprising if the front disappears entirely in subsequent model runs. High amplitude ridging builds overhead to end the week leading to what is expected to be an extended period of dry mid-winter weather.

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AVIATION

The leading edge of the precipitation next frontal system is approaching a roughly KBLI to KCLM line this morning, with gusty southerly winds ahead of the front and low MVFR ceilings and restricted visibility in rain along the frontal band. Expect increasing clouds and lowering ceilings spreading southeastward, with likely MVFR ceilings to cover the coast this evening and across the region by 12z Sunday. . Front moving into the area from the northwest will stall over the northwest portion of the area tonight and Sunday for rather consistent conditions through much of Sunday.

KSEA...VFR conditions through the afternoon with southeast winds around 6 to 9 kt, Expect lowering ceilings tonight with steadier rain and MVFR conditions expected 08-12z Sunday and continuing through much of the day.

MARINE

High pressure over the waters will weaken today. A front will move into the northern portion of the waters tonight and remain stationary into Monday. The front will lift north Monday night with high pressure rebuilding over the waters. The high will remain over the area through late in the week.

Small craft advisory winds along the coast, entrances to the Strait of Juan de Fuca, Admiralty Inlet and the Northern Inland waters for the most part through the weekend into Monday. Winds easing later Monday into Monday night.

Seas building to 10 to 15 feet today and tonight and to 12 to 18 feet Sunday. Seas beginning to subside Monday lowering to 9 to 11 feet Monday night and to 6 to 8 feet Tuesday. Felton

HYDROLOGY

No river flooding is expected through most of the weekend. Precipitation guidance continues to trend up leading to an increased concern for potential river flooding. The Skokomish River in Mason County is forecast to reach flood stage late Sunday night and crest in moderate flood stage Monday. For the remainder of the rivers, crest forecasts have increased significantly over the northern portion of the interior with the latest forecast run. While none of the rivers are currently forecast to reach flood stage, numerous rivers from King county northward are now forecast to crest in action stage Monday or Tuesday. In addition to the increasing precipitation amounts in the forecast, snow levels will rise from around 4500 feet later today when the precipitation starts to around 7500 feet by Monday night when the precipitation tapers off. Have added King, Snohomish, Skagit and Whatcom counties to the hydrologic outlook with the increase in the crest forecasts for possible flooding Monday and Tuesday. Mason county remains in the hydrologic outlook for the threat of flooding on the Skokomish beginning late Sunday.

This event is likely to be followed by a dry period, allowing for rivers to recede mid to late next week. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 2 PM this afternoon to 6 AM PST Monday for Grays Harbor Bar.

Small Craft Advisory until 6 AM 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-West Entrance U.S. Waters Strait Of Juan De Fuca.