textproduct: Seattle/Tacoma

SYNOPSIS

A trough and upper level low will move inland today into Friday, with rain and snow showers diminishing through today. A brief ridge will dry the region out later today into the first part of Friday. A blast of cold air from the Fraser River will keep temperatures chilly next couple of mornings, with wind chills into the low 20s and teens in many locations. Another low will dig down offshore from the Gulf of Alaska. The pattern will become active again this weekend into next week, with several rounds of rain, mountain snow, and gusty winds.

SHORT TERM /TODAY THROUGH SATURDAY/

A stacked upper level trough with an upper level low was located over the British Columbia/Washington border. This trough will spin an additional shortwave over the region this morning, which will interact with the stationary front over the central part of the state. The rain/snow showers in Snohomish County have diminished, and remnants of the complex from earlier are moving westward over north Clallam County this morning. The focus turns towards the south interior/south Puget Sound where additional bands of showers are moving north. The temperatures remain a few degrees above freezing in the Chehalis Valley/I-5 corridor (and this has kept the precipitation as rain). To the west in the Black Hills, it is closer to freezing and WSDOT cameras indicate snow on the sides of the roads on SR-8. To the north, northeast winds have picked up, bringing cooler Fraser River air into the north interior (down to as far as Clallam County). The cold weather advisory continues through late this morning for west Whatcom, San Juan, north Clallam, and also west central Snohomish Counties for wind chills in the low 20s to teens this morning.

The precipitation chances decrease substantially going into the afternoon as the trough moves east. This will be replaced with a brief ridge that passes overhead late tonight/Friday morning. Some cloud-free blue sky is possible later in the day (especially in the north interior and coast) - although highs will likely struggle to reach 40 for many today. The clear skies however will result in cool temperatures tonight as the Fraser air is reinforced by north flow behind the trough (though the outflow will weaken tonight). Wind chills/apparent temperatures are likely to become brisk again in the mid 20s, and may spread to other parts of the interior.

Friday will see a marginal warm up (highs returning into the low to mid 40s). The attention turns to the next low dropping down into the region from the Gulf of Alaska. Precipitation chances will increase for the Pacific Coast and Mountains late Friday into Saturday. As warmer air is brought in Saturday (highs closer to 50s), lowlands will only be expected to see rain with any showers, while mountains will see snow above 2,000 ft for the Cascades, and 3,000 ft in the Olympics. Precipitation amounts will be light for the day Saturday. Breezy offshore winds are expected Saturday, primarily in the Cascades and the Pacific Coast. Most likely gusts will peak around 25 to 35 mph. Lastly, seas are expected to increase offshore, with the potential for high surf conditions for beaches along the Pacific Coast Saturday and Sunday.

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

Most ensembles keep the low offshore this weekend into next week, with multiple rounds of precipitation continuing the remainder of the weekend into next week. Highs will remain in the low to mid 50s through this part of the forecast. The moisture content of the precipitation will increase on Monday and Wednesday. Hydrologic flooding impacts are not expected, but there remains potential for mountain snow with this system. There is lower confidence in heavier snowfall rates, as well as snow levels with the warmer air in place, but large-scale impacts are not expected with the snow being spread across several days (Wednesday is the only day where the snow may be heavy enough to produce possible travel impacts).

HPR

AVIATION

Southwesterly flow aloft will gradually become more northwesterly today as an upper level low continues to sink southward and then push inland into OR. Radar this morning shows wrap-around moisture from the surface low over the southern WA coastal waters currently making its way northward across the Chehalis River Valley and southern Sound this morning. A few lingering showers are also still present across the northern Olympic Peninsula as well. The majority of the showers continue to be rain early this morning, with the exception of KCLM which has been reporting light snow. Snow may continue to mix in with rain in any heavier shower activity through the morning hours, though do not expect any significant accumulations at any of the area terminals. Conditions at the terminals remain mixed early this morning, but generally more widespread MVFR/VFR, with a few spots of IFR/LIFR conditions in showers and patchy fog. Showers will taper in the afternoon for a return to overall VFR conditions.

Surface winds have transitioned to northerly overnight across the Sound terminals and increased to 4-8 kt. Gusty conditions, with winds to 30 kt, continue at KBLI as Fraser outflow persists through the morning hours. Fraser Outflow will weaken after 18Z and will generally keep the northern areas drier throughout the day.

KSEA...Conditions generally MVFR at the terminal this morning, though could see conditions drop to IFR/LIFR briefly in any shower activity or patchy fog. Conditions will improve back to VFR by the afternoon hours. Surface winds have become northerly at 4-8 kt, but will increase to 8-12 kt by 18Z.

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MARINE

A low pressure system located just south of the coastal waters will continue to move away from the area this morning. Meanwhile, strengthening high pressure over the interior of British Columbia overnight will continue to promote breezy Fraser Outflow across the Northern Inland Waters and Eastern Strait and easterly flow through the central and western Strait this morning. Fraser Outflow will ease late this morning as the high over British Columbia weakens, allowing for winds to ease below small craft criteria. Seas across the coastal waters will range between 5-8 ft.

Light offshore flow will then continue into early Friday with a broad surface trough over the coastal waters. A stronger system will move into the area waters over the weekend, increasing offshore flow and likely bringing southeasterly gales to the coastal waters. Seas look to build to 14-18 ft, though latest probabilistic guidance suggests that there is roughly a 40-50 percent chance of coastal seas building to greater than 18 ft. The pattern looks to remain active heading into next week, with additional systems moving across the area waters likely bringing additional rounds of headlines.

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HYDROLOGY

No river flooding is expected over the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Cold Weather Advisory until noon PST today for Lowlands of Western Whatcom County-San Juan County.

Cold Weather Advisory until 10 AM PST this morning for Downtown Everett / Marysville Area-Eastern Strait of Juan de Fuca-Island County-Lake Crescent Area Including US 101- Port Townsend Area-Western Strait of Juan de Fuca.

PZ...Small Craft Advisory until 10 AM PST this morning for Central U.S. Waters Strait Of Juan De Fuca-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.