textproduct: Seattle/Tacoma

SYNOPSIS

An upper level ridge will continue to build over Western Washington and persist through midweek, bringing drier conditions and patchy fog to the region. An active weather pattern may return as early as Thursday, bringing back lowland rain and mountain snow into the weekend.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

Latest satellite imagery shows mid to high level clouds moving over Western Washington this afternoon. As a result, the fog in the Chehalis Valley has struggled to scatter out this afternoon. An upper level ridge will be the prominent weather feature through at least midweek. This ridge will keep conditions dry across Western Washington. While conditions will remain dry, abundant lingering moisture may lead to patchy fog formation overnight, especially along the southern interior and Chehalis Valley. High temperatures will generally be in the mid to upper 40s. Low temperatures will be on the chilly side, with values in the low to mid 30s and upper 20s along the Chehalis Valley.

With an upper level ridge in place, stable conditions may develop and lead to an inversion on Tuesday and Wednesday. This may lead to stagnant conditions to develop. 29

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Long-range ensembles have the upper level ridge persisting over the region through at at least Wednesday, keeping conditions dry. Model solutions start to defer slightly on Thursday on the arrival of the next system. Depending on what scenario plays out, it will determine the next arrival of precipitation for the region. An active weather pattern is favored to continue into the weekend.

The threat of minor coastal flooding increases late in the week. While there is uncertainty in the timing and strength of the system, at this time it does not appear to exacerbate coastal flooding. 29

AVIATION

Northwesterly flow will persist aloft through the TAF period as a upper ridge level ridge builds into the region. A thermal trough at the surface will build along the coast on Monday, allowing for low level flow to transition to more east- northeasterly.

Mid to high clouds continue to stream in over the area as a frontal system moves into British Columbia this afternoon. As a result, low clouds and fog have not scattered out much for areas south of Puget Sound this afternoon. Conditions at terminals like KOLM in fog remain LIFR, while conditions elsewhere remain VFR this afternoon. Expect fog to redevelop and expand for areas south of the Sound into Monday morning. With cold overnight temperatures, terminals like KOLM will likely see another round of freezing fog overnight.

Winds remain light and variable for the majority of the area terminals this afternoon, however will transition to more northeasterly by tonight. The combination of mid to high level cloud cover and northeasterly winds may help mitigate fog development for terminals east of Puget Sound on Monday morning.

KSEA...VFR conditions with light northerly winds between 3-6 kt, transitioning to the northeast tonight. While a few low clouds will be possible within the vicinity of the terminal on Monday morning, northeasterly winds may help limit fog potential and keep VFR conditions prevalent at the terminal through the period.

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MARINE

High pressure will remain situated over the coastal waters through Wednesday. Meanwhile, a weak thermal trough will build along the coast on Monday. This will continue to promote offshore flow through the first half of the week. Seas ranging between 3-6 ft today will build to 6-9 ft late tonight into Monday as systems pass by to the north and a west-northwest swell moves into the coastal waters.

Dense fog may develop over portions of the interior waters with clearing conditions and light winds during the overnight periods the over the next few days and will likely restrict visibilities across the waters at times.

A more active pattern returns the second half of the week, with the next frontal system expected to move into the area waters on Thursday. This will allow for flow to transition back to southerly. Increasing winds and seas will likely bring the next round of headlines to the area waters.

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HYDROLOGY

No river flooding is expected during the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.