FXUS66 KSEW 161101 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 401 AM PDT Tue Apr 16 2024 .SYNOPSIS...Cool upper level trough over the area today will move east tonight. High amplitude upper level ridge building offshore extending into Northern British Columbia tonight and Wednesday. Weak upper level trough swinging down the backside of the ridge moving through Thursday. Upper level ridge building over Western Washington Friday will move east Saturday as a weakening front moves through the area. Another ridge will build into the Pacific Northwest Sunday into the first part of next week. && .SHORT TERM /TODAY THROUGH THURSDAY/...Satellite imagery shows cool upper level trough over the area this morning. Doppler radar indicating a convergence zone over Northern King county with isolated showers over the remainder of the area. Temperatures at 4 am/11z were in the upper 30s to mid 40s. Trough weakening as it remains over Western Washington today. Convergence zone staying intact this morning before dissipating this afternoon. The zone will wobble around between the northern half of King county and the southern half of Snohomish county. Scattered showers with the convergence zone with just isolated shower activity outside of the zone. With the trough overhead temperatures will remain cool with highs mostly in the lower to mid 50s. Trough moving east tonight with little shower activity there is left with the trough wrapping up in the evening hours. Skies clearing a bit with an upper level ridge building offshore. Air mass aloft still cool and with little wind in the lower levels good chance we will see freezing low temperatures in the Southwest Interior, southern end of the Hood Canal and into the Lower Chehalis Valley. Have issued a frost advisory for Wednesday morning between 2 and 9 am. Lows in the 30s. Upper level ridge continuing to build offshore into Northern British Columbia with dry north northwesterly flow aloft over the area. Temperatures warming after a cool start with highs a couple of degrees either side of 60. Ridge remaining in place Wednesday night. Weak and fairly dry upper level trough moving down the backside of the ridge into Western Washington Thursday. Low level flow turning weakly offshore Thursday pushing high temperatures mostly into the 60s. Lows Thursday morning in the 30s and lower 40s. .LONG TERM /FRIDAY THROUGH MONDAY/...Extended models in good agreement with upper level ridge rebuilding over Western Washington Friday. Low level flow still weak offshore. Friday looks to be the warmest day of the forecast period with highs in the 60s and the warmer locations near 70. Ridge shifts east Friday night into Saturday allowing a weakening front to move through by Saturday night. Not much left of this system by the time it reaches Western Washington so will just have chance pops Saturday afternoon and Saturday night. Surface and upper level ridge building behind the front Sunday. Low level flow switching to onshore behind the front will result in cooler high temperatures Sunday, near 60. A little warmer Monday as the ridge continues to build and the low level flow turns offshore with highs in the upper 50s to mid 60s. Felton && .AVIATION...A weakening convergence zone with light rain showers is continuing along the King and Snohomish county line early this morning. Additional showers are moving in along the coast. Most terminals are MVFR and VFR with variable to SSW surface winds. A westerly push through the Strait of Juan de Fuca will contribute to the direction of the surface winds changing for most terminals to be from the ENE by 12Z, lingering into this afternoon. VFR cigs AOA 045 likely to persist throughout the TAF period in the wake of any lingering shower activity in the morning. .KSEA...Convergence zone showers are largely to the north of the terminal early this morning, though currently MVFR with cigs AOA 025. Surface winds are still southwesterly at 10 kt, but are likely to turn more SE after 12Z. Between 18Z-20Z, a change to NW winds at 6-8 kt likely, becoming NE after 00Z. Cigs are expected to stay VFR after 14Z this morning. Kristell .MARINE...A westerly push down the Strait of Juan de Fuca will be concluding after 12Z this morning, with only marginal SCA winds in its wake until 18Z. Coastal seas range between 6-8 feet at 9 seconds and will come down late tonight to below 6 feet. High pressure is expected to build in for calmer waters through much of the rest of the week. Seas will come up again toward the weekend. Kristell && .HYDROLOGY...No river flooding expected in the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Frost Advisory from 2 AM to 9 AM PDT Wednesday for Hood Canal Area-Lower Chehalis Valley Area-Southwest Interior. PZ...Small Craft Advisory until 10 AM PDT this morning for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca. Gale Warning until 5 AM PDT early this morning for Admiralty Inlet-Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 10 AM PDT this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$