San Juan Islands and Northern Inland Waters Marine Forecast
|Tonight...Se Wind 5 To 15 Kt. Wind Waves 2 Ft Or Less.
|Thu...Se Wind 5 To 15 Kt Easing To 10 Kt In The Afternoon. Wind Waves 2 Ft Or Less.
|Thu Night...Light Wind. Wind Waves Less Than 1 Ft.
|Fri...Light Wind Becoming W To 10 Kt In The Afternoon. Wind Waves 1 Ft Or Less.
|Fri Night...Sw Wind To 10 Kt Becoming 5 To 15 Kt After Midnight. Wind Waves 2 Ft Or Less.
|Sat...Sw Wind 5 To 15 Kt. Wind Waves 2 Ft Or Less.
|Sat Night...S Wind 5 To 15 Kt Becoming To 10 Kt After Midnight. Wind Waves 2 Ft Or Less.
|Sun...S Wind 10 To 20 Kt Becoming Sw 15 To 25 Kt. Wind Waves 2 To 4 Ft.
|Mon...W Wind 5 To 15 Kt. Wind Waves 2 Ft Or Less.
| Area Forecast Discussion
...UPDATED National Weather Service Seattle WA
138pm PST Wednesday Feb 21 2024
A weakening low will continue to drift northward along the Washington Coast before dissolving on Thursday morning. Upper ridging will build into the region later Thursday with drier weather heading into the weekend. A more active pattern will enter the region on Sunday and continue into next week with a series of systems sliding across the Pacific Northwest.
* SNOW: A storm system will bring in heavy snowfall to the mountains towards the end of the weekend with accumulations of a foot or more across the mountain passes through Tuesday morning. Ensembles also hint at the possibility for areas of light lowland snow accumulations early Monday and Tuesday mornings from a rain/snow mix.
Short Term - Tonight Through Saturday
Light shower activity will continue to spread across western Washington today as a weakening stacked low stalls along the Pacific coast. With weak instability stemming from Seattle and Olympia southwestward across the Chehalis Valley, stronger convective showers that develop this afternoon may produce graupel and an isolated lightning strike or two. Temperatures today will peak right around normal, with most of the lowlands peaking in the lower 50s and snow levels above 4000 ft.
Moisture will continue to be injected into the region by the offshore low, maintaining steady light shower activity through early Thursday morning. Patchy fog and low stratus may develop Thursday morning with residual moisture at the surface. A drier air mass will push northward throughout the day Thursday as a ridge amplifies into the Pacific Northwest, allowing conditions to clear out and warm up several degrees. Fog and low stratus will likely redevelop overnight into Friday and clear out once again by the late morning. Temperatures will remain fairly steady on Thursday and Friday, with most lowlands peaking in the mid 50s.
Upper level flow will begin to flatten on Saturday as a trough begins to lower from the Gulf of Alaska. Cooler temperatures will cause snow levels to lower to 2500-3000 ft as precipitation spreads in from the north. The bulk of the moisture with this initial push will be focused over the Northern Cascades, with 2 to 4 inches of snow accumulation above 3500 ft through Saturday night with locally higher amounts over the highest peaks. Stevens Pass will likely see an inch of snowfall on Saturday, with the mountain passes southward favored to see minimal accumulations.
Long Term - Sunday Through Wednesday
A potent storm system will push into the Pacific Northwest on Sunday, bringing significant mountain snow to western Washington. The bulk of the moisture with this system will once again be centered over the Cascades, and moisture levels will be enhanced by breezy onshore flow. Widespread precipitation will continue through Tuesday morning with preliminary snow totals of up to a foot over the Olympics and 1 to 2 feet over the Cascades. Significant snowfall will likely cause impacts to travel, with a moderate (60 to 70 percent) chance of over 12 inches of snow through Snoqualmie Pass through Tuesday morning. Snowfall through Stevens Pass is favored to see heavier snowfall amounts, with a high (90 percent) chance of 12 inches of snow accumulation and even a low (20 percent) chance of seeing above 2 feet of snow through the pass. Latest ensemble guidance shows a mean snow accumulation forecast of up to 30 inches for the higher mountains of Snohomish County between Sunday and Tuesday, but snowfall totals remain fairly uncertain this far out.
While the primary concern of the extended period is heavy mountain snow, the lowlands are also primed to see a rain/snow mix at times Sunday night into the early part of next week. Precipitation will become more convective Sunday night into Monday, which may allow snow levels to lower towards the surface through evaporative cooling. Any lowland snow accumulations will likely occur on grassy or elevated surfaces and will quickly melt off with daytime temperatures in the 40s. The lowlands will likely see more of the same Tuesday morning before precipitation starts to taper off.
Western Washington will see little relief from wet and cool conditions on Tuesday with another storm system on track to cross the region on Wednesday. While this storm system looks to have less moisture than the weekend system, heavy snowfall is once again forecast over the mountains for mid-week. Temperatures will remain below average through much of next week across western Washington, with long-range ensembles favoring cooler and wetter conditions lasting through next week.
A stacked low/surface trough just off the Washington Coast continues to trigger light showers off the coast. Moderate showers continue to move over the Puget Sound Waters this afternoon, with some graupel potentially mixed in with the heaviest showers. Winds are beginning to die down in the coastal waters (though a couple gusts to 20 kt are still possible through the afternoon, will leave the small craft advisory in place up to 00Z). Additional gusty winds are still ongoing in the Admiralty Inlet and East Strait of Juan de Fuca this afternoon (will also keep that small craft advisory in place through 03Z).
Next significant system will approach the area Sunday into next week, with seas building and gusty winds expected across all waters. Seas will remain at 5 to 7 feet and increase above 10 feet Sunday into next week.
No river flooding is expected over the next 7 days.
NOAA Seattle WA Office: Watches - Warnings - Advisories
WA...None. PZ...Small Craft Advisory until 7pm PST this evening for
East Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory until 4pm PST this afternoon 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.