textproduct: Seattle/Tacoma

UPDATE

An atmospheric river continues to pour into the region this morning and will remain throughout the day. Rainfall has been observed from the mountains to the lowlands as snow levels are anywhere between 7,000 to 9,000 ft. Highs today will top out between the lower 50s along coast to the upper 50s in parts of the interior. Breezy southerly winds with gusts up to 20 to 25 mph throughout Puget Sound up towards Bellingham Bay. The previous discussion is below along with an updated aviation section:

SYNOPSIS

Atmospheric river will remain aimed at Western Washington through Friday with a cold front stalled over Vancouver Island. The river will come to an end as the cold front moves through the area Friday evening. Zonal flow aloft over the weekend with a weak system moving by to the north. Temporary break early Monday before additional systems arrive Tuesday and Wednesday.

SHORT TERM /TODAY THROUGH SATURDAY/

Satellite imagery shows long fetch of moisture extending from east of the Hawaiian Islands into Western Washington. Doppler radar indicating rain over most of the area with the rain shadow over the Central Puget Sound trying to get reestablished. Temperatures remaining mild with the clouds and rain, a couple of degrees either side of 50 at 2 am/09z.

No changes to the short term forecast this morning. Atmospheric river remaining over Western Washington with a cold front stalled over Vancouver Island through Friday. IVT values steady through the period, 500-700 kg/m/s. Little change in the snow levels as well in the 7500-9500 foot range. Breezy conditions at times with the front in the vicinity. Mild temperatures with the moisture tap all the way down to near Hawaii, mostly in the 50s through Friday.

Cold front moving through Friday evening ending the atmospheric river over the area. Steady rain turning to showers behind the front. Windy along the Strait of Juan de Fuca into Whidbey Island with a post frontal westerly push. Could see a brief convergence zone over Snohomish County early Saturday morning. Snow levels dropping quickly behind the front down to 3000-3500 feet with snow showers over all the passes but Snoqualmie. Lows in the mid 30s to lower 40s.

Snow levels continuing to fall Saturday to around 2000 feet. Moisture will be limited with just a chance of showers. For the lowlands post frontal onshore flow keeping skies mostly cloudy/partly sunny. High temperatures near the morning lows of the last few days, near 50. Felton

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

Weak system riding by to the north keeping chance or slight chance pops in the forecast Saturday night and Sunday. A little break in the weather Sunday night into Monday with a weak upper level ridge moving through ahead of the next weather system. Timing of the next system speeding up a little on the latest run by a few hours with rain starting Monday night. Frontal passage Tuesday with another system right on its heels for Wednesday. The Monday night and Tuesday system will push snow levels above the passes. Snow levels dropping down below pass levels Tuesday night into Wednesday. Highs in the lower to mid 50s cooling to near 50 Wednesday. Lows mid 30s to lower 40s except lower to mid 40s Tuesday morning.

AVIATION

Westerly flow aloft will continue into Friday with a stalled frontal boundary over Vancouver Island eventually pushing southeastward across the area on Friday. Ceilings across the region remain a mixed bag this morning with VFR to IFR conditions in light to moderate rain expected to persist through the day.

KSEA...Expecting an overall low confidence forecast for the TAF period as ceilings have been highly variable. Primarily MVFR ceilings continuing into tonight in light rain at times. Surface winds southerly 8 to 12 knots.

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MARINE

Periods of Small Craft southerlies will continue across the waters late into the week as a frontal system remains stalled over Vancouver Island. The frontal system will move over area waters on Friday, with a westerly push through the Strait of Juan de Fuca expected to reach potential gale force strength. Winds will ease into the weekend as a building surface ridge offshore moves inland. Another potent front will arrive Monday night into Tuesday.

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HYDROLOGY

Even with the atmospheric river aimed at Western Washington rainfall amounts have not been that excessive. In the last 6 hours ending at 2 am/09z rainfall totals in the 0.30 to 0.60 inch range over the Olympics and Northern and Central Cascades. Southern Cascades and lowlands less than 0.30 inches. Wettest location has been along the coast with 0.60 to 1 inch of rain. Rainfall totals for the last 24 hours more impressive with 1.5 to 3 inches over the Northern Cascades and Olympics, one to two inches along the coast. The off and on rain shadow over the Central Puget Sound has kept rain totals down to 0.10 to 0.50 inches.

Little change in the pattern through Friday with another 2 to 4 inches of rain in the North and Central Cascades and over the Olympics. Snow levels remaining elevated, 7500 feet to 9500 feet. Steady rain will give way to showers and much lower snow levels when the cold front moves through Friday evening.

Flood warning already up for the Snoqualmie, Snohomish, Skykomish and Tolt rivers. These rivers have either crested or will crest later today as a result of the lower rainfall rates in the Central Cascades overnight. The Tolt, Skykomish and upper reaches of the Snoqualmie have already receded below flood stage. The lower reaches of the Snoqualmie as well as the Snohomish will begin receding later today. Rainfall rates in the mountains increasing this afternoon with the higher rates continuing into Friday. This will create a double crest scenario Friday afternoon or Friday evening pushing the rivers back above flood stage.

In addition to the rivers in King and Snohomish county, a flood watch will also remain in effect for Skagit and Whatcom county. The reduced rainfall rates overnight have lowered the chances of the Skagit at Concrete reaching flood stage this afternoon but with the increasing rainfall later today there is still a good chance the river reaches flood stage Friday. Same is true downstream for the Skagit at Mount Vernon. Farther north the Nooksack at Ferndale is forecast to crest a few inches below flood stage Friday.

Last but not least, the Skokomish river in Mason county has been underperforming so far but with another round of warm rain coming up it is certainly possible the river gets to flood stage later today or Friday. The watch for Mason county will also remain in effect. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...Flood Watch through Friday afternoon for 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-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 the North Cascades- Foothills of the Western and Southern Olympic Peninsula- Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties- Lowlands of Western Whatcom County-Middle Chehalis River Valley-Olympia and Southern Puget Sound-Olympics- Shoreline / Lynnwood / South Everett Area-Southern Hood Canal-Willapa and Black Hills.

PZ...Small Craft Advisory until 5 PM PDT this afternoon for West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 AM PDT Friday 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.