textproduct: Seattle/Tacoma

SYNOPSIS

An upper level ridge will continue building over Western Washington and remain in place through midweek. This will maintain dry conditions and patchy fog. A more active weather pattern returns on Thursday, with a return of mountain snow and lowland rain late this week through the start of next week. An increased threat of coastal flooding due to larger high tides develops late this week.

SHORT TERM /TODAY THROUGH WEDNESDAY NIGHT/

Mid to high clouds continue to move over Western Washington this afternoon. Foggy conditions have been slow to improve across the southern interior, but may see some brief improvement late this afternoon. The forecast remains on track with the upper level ridge remaining over the region through Wednesday, maintaining drier conditions. In addition, patchy fog is possible overnight, but easterly winds downsloping across the Cascades and mid/high clouds will likely hinder widespread fog development. The exception being the Chehalis Valley and any areas that clear out overnight. Chilly nights expected to continue through midweek, with low temperatures in the low to mid 30s and upper 20s in the Chehalis Valley. High temperatures will be in the mid to upper 40s.

With an upper level ridge in place over the region, stable conditions may develop and lead to an inversion on Tuesday and Wednesday. These conditions combined with light winds may lead to stagnant conditions over portions of the region. 29

LONG TERM /THURSDAY THROUGH SUNDAY/

There is good agreement between ensemble guidance that the ridge axis will push out of the region on Thursday towards the Rockies. An upper level trough digging off the coast of California will lift into the region on Thursday, bringing back lowland rain and mountain snow. Model solutions continue to differ slightly on Thursday on the timing of the next system. The European model has the system arriving quicker on Thursday morning, while the GFS is slower and has the system arriving Thursday evening. An active weather pattern is favored to continue into the weekend and early next week, with additional systems expected to move over the region.

The threat of minor coastal flooding will continue to increase late in the week. While there is uncertainty regarding the timing and strength of the upcoming weather systems, they could exacerbate coastal flooding concerns. 29

AVIATION

Northwesterly flow aloft will gradually become more westerly into Tuesday with the ridge axis pushing eastward. Meanwhile, low level flow below 5000 ft continues to become southerly tonight through Tuesday morning. This maintains predominantly VFR conditions across the area this evening with passing high clouds. Notably, patches of IFR fog/low stratus linger south of Puget Sound. Surface winds will persist from the north/northeast at 4 to 6 kt for most. Fog will redevelop and expand in coverage for areas south of the Sound tonight and cold temperatures near freezing will likely yield another round of freezing fog for terminals like KOLM. However, much like this morning, the combination high clouds and northeasterly surface winds may limit the extent of fog development for terminals east of Puget Sound Tuesday morning. Surface winds gradually transition back to southerly by late Tuesday afternoon.

KSEA...VFR conditions with passing high clouds and NE winds around 6-8 kt this evening. Winds will become increasingly southerly through the day Tuesday. Some low clouds could develop in the vicinity of the terminal Tuesday morning, expect northeasterly winds to limit fog potential and maintain likely VFR conditions at the terminal through the period.

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MARINE

High pressure will remain situated over the coastal waters through Wednesday, while a weak thermal trough remains situated along the coast into Tuesday. This will continue to promote offshore flow through the first half of the week. Seas will continue to hover between 6-9 feet today into Tuesday with a west-northwest swell moving into the coastal waters. Seas will then gradually subside towards 5-7 feet by midweek.

Dense fog may develop over portions of the interior waters with clearing conditions and light winds during the overnight periods the next few days and may 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, followed by a stronger system on Saturday. Increasing winds and seas building to 10-15 feet by the weekend will likely bring the next round of area-wide headlines.

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HYDROLOGY

No river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

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