textproduct: Seattle/Tacoma

SYNOPSIS

The thunderstorm threat will widely diminish on Sunday. Another trough will move across the region late Monday into Tuesday. A warmer and drier trend is then expected mid to late week as a ridge starts to build into the region, however shower chances may increase again by Friday and into Saturday as a disturbance approaches from the west.

SHORT TERM /TODAY THROUGH TUESDAY/

Broad troughing remains over the NE PAC while vast ridging resides upstream, nosing into the PNW today. Marine stratus again filling up across W WA as mid-high level clouds track overhead so far this morning. A chance (15-25%) of thunderstorms is forecast for the North Cascades with lesser probabilities elsewhere given NBM prob thunder. Monday's forecast is quite similar in regards to convection but probabilities should remain capped at 10-15%, likely due to more large-scale subsidence provided by more pronounced ridging overhead. Highs for Sunday and Monday in the mid 70s to mid 80s with overnight lows in the lower to upper 50s. Coastal area highs are forecast in the 60s.

A rather typical pattern of onshore low-level flow maintaining morning clouds, with some clearing in the afternoon on Tuesday. A passing trough could provide a reinforcing push of clouds and knock temperatures down a few degrees, mainly for the SW interior. Otherwise, benign conditions are in store with highs in the mid 70s to lower 80s across the interior and 60s along the coast. Overnight lows are forecast into the 50s area wide.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

An upper-ridge looks to build across the region during the second half of the week. Continued low-level onshore flow will help to keep temperatures from warming too aggressively. The pattern will then begin to change towards Friday and Saturday as ensemble guidance suggests the next disturbance may get close enough to bring another round of shower and potential thunderstorm chances. And with that, temperatures could cool below average for the first time in a while.

AVIATION

The upper level trough over southwestern B.C. will retrograde offshore but maintain southwesterly flow across the area. Low to mid level stratus has developed across most of western Washington early this morning. Much of southwest Washington is under MVFR ceilings, through expect areas northward to eventually see a lowering to MVFR through the early morning hours. Probabilities are very low (10% or less) for any of the TAF sites to see IFR or lower ceilings. Stratus should slowly scatter in the late morning hours, scattering between around 19-21Z. Stratus will likely remain in place along the immediate coast and set the stage for a more traditional marine push late tonight into Monday morning. Light southwest to west winds prevail this morning, increasing in the afternoon to around 5-10 kt. Winds through the Puget Sound will shift to northerly by around 19- 21Z and through the evening.

KSEA...Ceilings will continue to lower this morning to MVFR through much of this morning. Probabilities are very low (<8%) for IFR or lower conditions. Stratus should begin to lift and scatter to VFR after 19-20Z with decreasing clouds through this evening. Stratus is expected to return again after 12Z Monday. Southwest winds 5-8 kt will continue through this morning, turning to become more northwesterly after around 19-21Z and persist through this evening. 62

MARINE

Broad high pressure will redevelop over the far offshore waters today and strengthen going into next week, maintaining northwesterly winds over the coastal waters. Seas look to rise to around 4-6 ft tonight. Seas then look to become steeper Monday night into Tuesday to around 6-8 ft at 7 seconds as winds increase over the outermost coastal waters. Steep seas look to continue through Thursday.

Diurnally driven westerly winds will continue to occur each afternoon and evening through the Strait of Juan de Fuca. The strongest push looks to be tonight, for which a Small Craft Advisory has been issued. The westerly pushes will gradually weaken through the week with additional headlines unlikely at this time. 62/29

FIRE WEATHER

Convection will be largely confined to northern Cascade crest where a 15-20% chance of thunderstorm is in the forecast according to the NBM. Continued onshore flow and excellent overnight humidity recoveries will then help mitigate fire weather conditions to start the week. While some uncertainty remains in the long term pattern, ensemble guidance has increasingly come to consensus that a warming and drying trend is likely mid to late week, before the potential for shower and thunderstorm chances increases again late week as the next disturbance approaches from the west. This could potentially reintroduce some elevated fire weather concerns to the area.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 AM PDT early this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 4 PM this afternoon to 3 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.