FXUS66 KSEW 181537 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 837 AM PDT Sat Jul 18 2026 .SYNOPSIS... Weak upper level trough over the area today will move northeast Sunday. Seasonable temperatures over the weekend with some morning clouds. High pressure builds over Western Washington Monday with the ridge remaining in place through Wednesday giving the interior much above normal temperatures. Ridge weakens Thursday with an upper level trough approaching Friday bringing cooler temperatures to the region. && .SHORT TERM /TODAY THROUGH MONDAY/... No major updates have been made this morning. See below for an updated aviation discussion. Weak upper level trough hanging over the area today with light flow in the lower levels. Without any ridge building/subsidence will have to rely on the mid July sun to dissipate the stratus. Stratus layer not very thick, 1000 feet or less in most places, making for a late morning/midday breakout over the interior. Stratus hanging tougher along the coast into the afternoon hours. Highs mid 60s along the coast and 70s over the interior. Weak upper level trough over the area tonight lifting northeast Sunday. Marine layer not as thick Sunday morning with less morning cloud cover and more sunshine by late morning. Highs warming a little, near 70 along the coast and mid 70s to mid 80s over the interior. Lows tonight in the 50s. Upper level ridge well to the southeast beginning to build back to the northwest towards Western Washington. 500 mb heights rising into the mid 580 dms Monday with 500 mb temperatures warming to plus 18 to 20C by 00z Tuesday. Low level flow turning light offshore. Highs warming into the 80s and lower 90s over the interior with 70s to lower 80s for the coast. Minor HeatRisk over the weekend with moderate HeatRisk over most of the interior Monday. Felton && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Models in good agreement with the upper level ridge remaining over Western Washington through Wednesday. High in the 80s to lower 90s over the interior with 70s to lower 80s along the coast. Not expecting any record highs with the much above normal temperatures. Seattle records Tuesday and Wednesday both from 2006 ( 97 Tuesday and 96 Wednesday ). Lows in the 50s and lower 60s. Moderate HeatRisk for the interior for both days with a 30-50% chance of major HeatRisk for the Central and Southern Puget Sound. Upper level ridge weakening Thursday with the low level flow going light onshore. Highs much cooler on the coast, mid 60s to lower 70s. For the interior 5 to 10 degrees of cooling with highs in the upper 70s to upper 80s. Not a lot of consistency in the solutions for Friday. The operational ECMWF has the much weakened remnants of what is now tropical storm Elida just offshore. The GFS has a weak trough moving through with increasing low level onshore flow. The blend just has a continuation of the weak marine push that started Thursday. Confidence low so will trend the forecast towards climatology with highs mid 60s coast and 70s inland. Felton && .AVIATION... Westerly flow aloft will continue across Western Washington today as an upper trough over southern British Columbia gradually progresses eastward. Broken MVFR to IFR cigs across the area this morning will start to erode later this morning, giving way to VFR conditions for the afternoon and evening. Another round of stratus is on track to redevelop and push inland once again tonight into Sunday morning. It will most likely remain just west of the metro area, but there is a 25-30% chance of seeing MVFR or lower cigs in the Seattle metro from around 12-17Z Sun. Winds remain west to northwest along the coast, with winds in the interior turning from light south to northerly 5-10 kt by this evening. A few gusts to 15 kt will be possible at CLM this evening. KSEA...IFR cigs under broken stratus should begin to erode after 18- 19Z this morning, giving way to VFR conditions through the rest of the day. Another round of low ceilings will be possible with a 20- 25% chance of seeing MVFR or lower conditions between 12Z-17Z Sun. Surface winds light S/SW will veer W/NW 5 to 8 knots this afternoon then northerly tonight. 27/62 && .MARINE... A broad surface ridge centered well offshore will expand eastward this weekend. This will increase onshore flow somewhat later today into tonight with small craft advisory westerlies developing in the central/east strait as well as gusty northwesterlies and choppy seas for the outer coastal waters. Thermally induced surface low pressure is expected to deepen across the interior of Western Washington Monday through Wednesday. This will lead to varying degrees of onshore flow into the middle portion of the coming week. 27 && .FIRE WEATHER... Fire weather concerns increasing as high temperatures warm to much above normal the first part of next week. While the low level flow does not go offshore for a prolonged period of time relative humidity values in the afternoon will drop below 30% in the foothills as well as the Central and Southern Puget Sound Monday through Wednesday. The very warm and dry conditions beginning Monday has the potential for increasing fire activity from any new lightning starts from Thursday's convection. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 1 AM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory from 5 PM this afternoon to 11 AM PDT Sunday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. && $$