textproduct: Seattle/Tacoma

SYNOPSIS

Dry conditions will persist through early Thursday as an upper level ridge builds over Western Washington, bringing the chance for morning fog or low stratus. The ridge will weaken late Thursday as the next frontal system arrives, bringing lowland rain and mountain snow. Unsettled and cooler conditions continue into the weekend, with additional systems expected to move over the region.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

Satellite shows mostly clear skies across the area this evening, with some spots of fog developing across portions of the southern Sound. Expect the extent of morning fog/low clouds to expand heading into early Wednesday as a weak upper level ridge settles over western Washington. Improvement is expected by late morning or early afternoon to mostly clear skies with high temperatures in the upper 40s to low 50s. The upper level ridge will begin to flatten Thursday evening as the next frontal system approaches. With the ridge still in place Thursday morning, another round of fog/low clouds is likely. Cloud cover will increase inland Thursday afternoon as the frontal system arrives to the coastline. 29/14

LONG TERM /FRIDAY THROUGH TUESDAY/

The aforementioned frontal system will continue into Friday bringing widespread lowland rain and mountain snow. There is good agreement between ensembles that the weather pattern will remain unsettled into the weekend and into early next week. In addition, model guidance continues to highlight an upper level trough digging southwards into California on Sunday, opening the opportunity for a colder air mass to settle over Western Washington through Tuesday. This may bring the potential for snow to mix with rain at the lower elevations during the overnight hours. However, at this time no accumulation is expected for the lowlands given that PoPs will be generally less than 30% and QPF amounts are less than 0.05 inches. 29

AVIATION

Weak high pressure will nudge inland tonight and Wednesday for dry and stable conditions. The flow aloft is westerly, becoming northerly on Wednesday morning. Surface winds will be NNE through the TAF period. Low clouds and fog will redevelop overnight and mainly impact areas around the south sound. Low clouds and fog will dissipate by 18-20Z with VFR conditions expected. 33/21

KSEA...N winds 8-12kt with VFR conditions overnight. Patchy low clouds in the vicinity 12-16Z becoming clear thereafter. 33/21

MARINE

High pressure will continue building over area waters through Thursday morning, bringing calm marine conditions. A front will move over the waters late Thursday into Friday, with additional systems possible into the weekend and early next week.

Seas 7 to 8 ft this afternoon will continue decreasing to 5 to 6 ft by Wednesday and begin to rise Thursday afternoon, building as high as 13-17 ft early Friday morning. Seas will gradually decrease Friday evening, hovering between 8 to 10 ft through early next week. 29

HYDROLOGY

River flooding is not expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

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