textproduct: Seattle/Tacoma

SYNOPSIS

Multiple weather systems will move across the area through early next week due to continued upper troughing offshore. Lowland rain, high elevation mountain snowfall, breezy winds, and coastal flooding are expected at times into Monday. Another system will move across Western Washington Tuesday into Wednesday.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

Light precipitation continues to spread northwards across Western Washington this afternoon ahead of a frontal system. However, continued drier air at the surface has resulted in mainly light amounts, primarily south of Seattle. Lowland rain will increase tonight into Friday morning with the frontal system along with a moistening airmass. The main concern through Friday will be continued wintry mix over the Cascades, including the Cascade Passes. Temperatures will continue to warm aloft tonight, but east flow at the Cascade Passes (particularly Stevens and Snoqualmie) will result in temperatures remaining near or below freezing into Friday morning. Freezing rain will continue overnight for both Passes (in addition to White Pass this evening), with light snowfall at the onset for Stevens Pass. A Winter Weather Advisory remains in place through Friday morning for Snoqualmie and Stevens Pass. If you're traveling over the Passes through Friday, monitor WSDOT for road conditions and information.

Generally light precipitation expected Friday afternoon into Friday night before the next weather system moves northwards into the area on Saturday. South winds will increase Saturday, becoming breezy at times for Whidbey Island northwards and along the coast, with gusts in these areas ranging 25 to 35 MPH. Snow levels will also remain elevated on Saturday, around 4500 to 5500 feet for high elevation mountain snowfall, and rain or a rain/snow mix for the Passes.

Coastal flooding concerns also increase going into the weekend due to abnormally high tides. Initially, coastal flooding is expected along the coast Friday and Saturday, where a Coastal Flood Watch has been issued. Moderate coastal flooding is forecast both days, with major coastal flooding possible on Saturday for Grays Harbor County.

A compact low pressure system will then drift northwards Saturday night into Sunday. More information can be found in the long term section regarding this system. Highs on Friday and Saturday will warm into the upper 40s to low 50s.

LONG TERM /SUNDAY THROUGH THURSDAY/

A surface low will strengthen offshore of northern California and Oregon late Saturday into Saturday night and track northwards into Sunday. There remains continued uncertainty into the placement and intensity of this surface low by Sunday morning. This especially impacts the wind forecast Saturday night into Sunday. The spread in the 10-90th PCT wind gusts from NBM remains quite large.. ranging 25-55 MPH for the coast and north interior, and 25-45 MPH for Puget Sound. The variation in low placement can also be seen well in the UW WRF GFS ensembles, with individual members showing the low location offshore, and others further inland. Additional hi-res guidance (HREF/REFS) will come into range over the next 12-24 hours, and the wind forecast will continue to be refined. Continue to monitor the forecast during this period in regards to potential impacts.

In addition to the winds, coastal flooding concerns will likely peak on Sunday, particularly due to weather exacerbating the issue (i.e. lower pressure, stronger winds). Major coastal flooding is once again possible Sunday for the coast, with widespread minor to moderate coastal flooding for the interior. Water levels look to rise up to a maximum of around 2 to 2.75 feet above ground level over the weekend, and up to 3 feet along the coast.

The aforementioned system will move through on Sunday, with another round of lowland rain and mountain snow expected on Monday as an upper trough progresses east over the Pacific Northwest. There may be a break in the action Monday night, however, another frontal system looks likely Tuesday into Wednesday. Ensembles suggest another round of lowland rain, potentially heavier mountain snow, and breezy winds. JD

AVIATION

Mainly southwest flow aloft throughout the period as an upper- trough remains offshore. Low-level flow light but is gradually increasing in magnitude out of the south into early Friday morning. Showers are moving through most of the terminals this evening. Areas of IFR/LIFR will return overnight with the arrival of steadier rainfall lowering cigs and vis. IFR/LIFR conditions will persist into Friday with minimal improvement into the afternoon. Winds generally light, but increasing around 4-8 kt out of the E-SE into Friday for locations such as KOLM and KHQM.

KSEA...Rain showers are moving through the terminal this evening, with ceilings and visibilities dropping to MVFR. High confidence that a prolong LIFR ceiling (with lower VIS from mist) will form later tonight into much of Friday, with improvements to MVFR not taking shape till late in the afternoon. Surface winds generally light and variable, becoming more consistent out of the SE on Friday between 2- 5 kt.

McMillian/HPR

MARINE

A weak system is moving into the region from the south tonight into Friday morning. Little to no impacts are expected but a much stronger disturbance is in line to arrive Saturday into Sunday morning for increasing winds and seas. Here we'll see the next best chance of widespread headlines with SCA winds. Can't rule out the potential for gales. Another system will arrive Monday followed by an additional disturbance on Tuesday as the pattern looks to remain into next week.

Seas 5 to 8 feet building to 10 to 14 feet Saturday. Seas subsiding back down below 10 feet Monday but could rise again towards midweek.

McMillian

HYDROLOGY

Multiple frontal systems will move through Western Washington into next week. The Skokomish River, starting from elevated levels, is forecast to approach flood stage later on Sunday, before slowly receding next week. No additional river flooding is expected into next week. JD

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 7 AM PST Friday for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County.

Coastal Flood Watch from Saturday morning through Saturday afternoon for Grays Harbor County Coast-Northern Washington Coast.

Coastal Flood Warning from 9 AM to 1 PM PST Friday for Grays Harbor County Coast.

PZ...None.