####018006284#### FXUS66 KSEW 101645 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 945 AM PDT Fri May 10 2024 .SYNOPSIS...Upper level ridge over Western Washington today with low level offshore flow. The ridge will weaken Saturday with the low level flow turning onshore. Ridge moving south Sunday with a weak system moving through the area late Sunday into Monday. Ridge rebuilding Tuesday. Unsettled weather possible for the middle of next week. && .SHORT TERM /TODAY THROUGH SUNDAY/...Clear skies on visible satellite this morning across the entire region. Temperatures are quickly rising with light offshore flow, with many inland locations already pushing 70F as of 9:30 am. Warming trend continuing today with an upper level ridge over the area. Surface gradients offshore but not very strongly with the cross cascade gradient near 0. Temperatures aloft warming today with 850 mb temperatures in the plus 14 to 16C range by late this afternoon. Winds at 850 and 700 mb light easterly all day. High temperatures warming 5 to 10 degrees in most locations putting highs in the 70s to mid 80s inland and upper 70s to mid 80s along the coast. Northerlies picking up over the Puget Sound this afternoon will knock a couple of degrees off the highs near water. Subtle changes in the pattern tonight. Offshore gradients weaken with cross cascade gradient going positive overnight. The weakening easterlies overnight will give the area more uniform low temperatures, in the lower to mid 50s. Saturday remaining warm for the interior. The question is how warm? Is it a fake out day, winds turn onshore but not early enough and highs are a little warmer than the day before, or the the onshore flow get inland enough to bring a round of slight cooling to the interior. Going with the latter this morning. In addition to the low level flow turning onshore Saturday the ridge aloft weakens ( 850 mb temperatures cool a couple of degrees to the plus 12 to 14C range ) and the winds at 850 and 700 mb are westerly from the get go. Still going to be a warm day with highs over the interior in the lower 70s to lower 80s. With onshore flow all day the coast will be much cooler, highs in the 60s. Upper level ridge continues to weaken Saturday night into Sunday with a weak shortwave approaching the area by late Sunday afternoon. Low level onshore flow increasing Saturday night into Sunday. Stratus along the coast Saturday night moving inland Sunday morning stopping just short of the Puget Sound. After lows in the mid 40s to lower 50s highs Sunday much cooler over the interior with 60s and lower 70s. Highs along the coast only in the lower 60s. .LONG TERM /MONDAY THROUGH THURSDAY/...Weak shortwave moving through Sunday night into Monday. Shower chances with this feature confined mostly to the mountains. Under mostly cloudy skies high temperatures will cool back to a little below normal, in the upper 50s to mid 60s. Upper level ridge rebuilding Tuesday. Onshore gradients becoming northerly in the afternoon. With more sunshine highs warming into the 60s and lower 70s. Confidence beyond Tuesday very low. Model blend has chance pops over the area beginning Tuesday night and continuing through Thursday. The operational GFS builds an upper level ridge over the area Wednesday and Thursday. The ECMWF also has a ridge for Wednesday with the ridge breaking down Thursday as a front approaches from the northwest. Ensembles in good agreement with the operational runs Tuesday night and Wednesday with only a couple of the ensemble solutions wet. The GFS ensembles remain completely dry Thursday while the ECMWF ensembles are split between wet and dry solutions. Took the chance pops out of the Tuesday night forecast. Will leave the blend slight chance pops in for Wednesday and Thursday for now. If the signal from the ensembles is as strong as tonight look for the pops to get taken out of the Wednesday forecast. The inconsistency with the pops extends to the temperatures as well. Both Wednesday and Thursday the likely high temperature ranges are over 20 degrees for Seattle. Given the ensemble solutions will lean the high temperatures a little above normal instead of going with just climatology with 60s and lower 70s Wednesday and Thursday. Felton && .AVIATION...Light east wind aloft turning west as an upper-level ridge begins to deamplify over western Washington. VFR conditions with mostly clear skies through the TAF period. A few thin high cirrus clouds will pass through the northern parts of the region. Surface winds will peak this afternoon at 4 to 8 kt, becoming light and variable tonight. KSEA...VFR with mostly clear skies, a few high clouds. North winds 4 to 8 kt with a couple gusts possible this afternoon, before diminishing this evening. HPR/LH && .MARINE...High pressure over the region with a thermal trough along will shift inland today and into Saturday. As it breaks down, offshore flow on Friday will revert to onshore flow Saturday. Winds for Friday remain light with a mix of offshore/northerly winds. Couple gusts to 15 kt are possible in the Strait of Juan de Fuca/Puget Sound/Outer Coastal Waters. A trough to the north in Canada will send a push down the coastal waters and Strait of Juan de Fuca. With gales possible in the Central/East Strait, a gale watch was issued from Saturday afternoon through first part of Monday. Expect the onshore pattern to continue into next week. Seas will generally range 5 to 7 feet into Saturday, briefly building to 8 to 9 feet for the outer Coastal Waters over the Saturday into Sunday. HPR/LH && .HYDROLOGY...The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated as needed. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Gale Watch from Saturday afternoon through Monday morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$