


Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
632 FXUS66 KSEW 151022 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 322 AM PDT Tue Jul 15 2025 .SYNOPSIS...Upper level ridge over the area today will weaken later Wednesday. Low level offshore flow developing today continuing into Wednesday. Low level flow turning back onshore Wednesday afternoon into Thursday as a weak upper level trough moves by to the northeast. Low level onshore flow pattern continuing into the first part of next week keeping temperatures a little below normal with varying degrees of late night and morning low clouds. && .SHORT TERM /TODAY THROUGH THURSDAY/...Satellite imagery shows stratus over the southern portion of Grays Harbor county right up to the Thurston county border and a few clouds over the Cascades. Clear skies for the remainder of the area. Temperatures at 3 am/109z were in the 50s to lower 60s. Open those windows up and let some cool air inside. It`s going to be in short supply the next couple of days. Upper level ridge building over Western Washington today with a thermally induced surface trough moving up from Oregon in the afternoon with the low level flow turning offshore. High temperatures will be about 10 degrees warmer than Monday, in the mid 70s to mid 80s along the coast and 80s to lower 90s inland. Low level offshore flow continuing overnight. Cross Cascade gradient going negative in the evening and remaining negative into Wednesday morning. The resulting light/easterly surface winds will keep lows in the 60s in locations exposed to the easterlies like the Cascade foothills. Locations without any easterly wind dropping into the upper 50s. Wednesday will be the warmest day of the next week. Temperatures aloft peaking with model 850 temps in the plus 17C to plus 20C range. Thermally induced surface trough over the area in the morning will move east of the Cascades in the afternoon. This transition to onshore flow will cool the coast down in the afternoon but over the interior just create light winds which will allow high temperatures to warm into the 80s to mid 90s. Highs on the coast in the 70s will occur in the middle of the day. Not expecting any records Wednesday. There have been a couple of very hot July 16ths in Western Washington. On July 16th 1979 Seattle had a high of 98 degrees tied for the 9th warmest day on record at Seattle Tacoma airport. There was a hotter July 16th before Seattle-Tacoma airport was built. In 1941 the high at the Federal Building in downtown Seattle was 100 degrees. The only time between 1894 and 1944 when the Federal Building was the official Seattle weather station that the mercury reached 100 degrees. It was hot all across Western Washington. Olympia reached 103 degrees which was the warmest day on record in Olympia until the 104 degree day on August 9th, 1981. The 103 degrees on July 16th, 1941 is still tied for the 5th warmest day in Olympia. Upper level ridge weakening Wednesday night but the low level onshore flow is not very strong. Southwesterly surface winds with a shallow layer of marine air will provide some relief in the early morning hours with lows dropping into the 50s. Zonal flow aloft combined with weak low level onshore flow creating a weak marine push scenario Thursday. Low clouds along the coast will move inland early but likely remain west of Puget Sound. Highs 5 to 10 degrees cooler over the interior, in the upper 70s to mid 80s. With onshore flow all day highs on the coast will have trouble getting out of the 60s. No change to the HeatRisk across Western Washington early this morning with moderate HeatRisk over the interior today and tomorrow. The heat advisory will go into effect at 10 am this morning and will remain in effect through 10 pm Wednesday. .LONG TERM /FRIDAY THROUGH MONDAY/...The main theme for the extended period is a few days of slightly below normal temperatures after Friday. Models in general agreement with the low level onshore flow pattern continuing through the period in varying degrees. Zonal flow aloft giving way to some weak trofiness Sunday into Monday. This will deepen the marine layer over the interior potentially making Sunday the coolest day. This feature could also produce a late day shower over the North Cascades. Highs in the 70s and lower 80s Friday lowering to the upper 60s to mid 70s Sunday and Monday. Felton && .AVIATION...Northerly flow aloft as upper level ridging remains offshore. VFR conditions for all terminals this morning will continue throughout the TAF period. KHQM may see a brush of MVFR stratus early this morning, but confidence is low and will most likely remain VFR. Light N/NE winds across the area will increase this afternoon to 8 to 12 knots, with the potential of a few gusts reaching 20 kts at times. KSEA...VFR conditions throughout the TAF period. Northerly winds this morning 4 to 8 knots will increase after 18z to 9 to 14 knots with a few gusts potentially reaching 20 kts throughout the afternoon. Winds look to remain elevated throughout the evening before gradually decreasing overnight. Mazurkiewicz && .MARINE...High pressure remains offshore this morning. A small shift this morning will bring offshore winds throughout the area waters. Onshore flow will return late Wednesday evening with the potential of Small Craft Advisory winds through the Strait. Northerlies will increase periodically over the coastal waters through midweek as a thermal trough builds over the coast - which may bring SCA conditions at times which will need to be monitored. Combined seas this morning 7 to 9 feet will lower slowly to 6 to 8 feet by Wednesday and continue to lower to 4 to 6 feet by the weekend. Mazurkiewicz && .FIRE WEATHER...High pressure returns to the area today. Afternoon RH values will lower to critical thresholds with a thermal trough building north. While some uncertainty remains to how far north and west the trough builds, expect to see at least some light east component to the surface winds near the Cascade gaps in zone 659 and portions of 657 and 658 beginning this afternoon. A Fire Weather Watch for these areas remains in effect. Confidence is lower in seeing more widespread easterly wind, but this may serve to further reduce RHs. Depending on the placement of the thermal trough, expect to see a deeper mixed layer and increased instability over the Cascades with mixing heights potentially rising into Wednesday. Today and Wednesday will have the worst fire weather conditions for existing incidents and the potential for any new ones if they were to begin. Cooling trend beginning Thursday with temperatures dropping below normal Saturday. Minimum RH values increasing Thursday into the weekend with the return of low level onshore flow. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Fire Weather Watch from 11 AM PDT this morning through Wednesday evening for Black Hills and Southwest Interior Lowlands- West Slopes of the Central Cascades Generally above 1500 Feet-West Slopes of the North Cascades Generally above 1500 Feet. Heat Advisory from noon today to 10 PM PDT Wednesday for City of Seattle-Downtown Everett / Marysville Area-Eastern Kitsap County-Eastside-Foothills and Valleys of Central King County-Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Snohomish and Northern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Foothills and Valleys of the North Cascades- Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-Middle Chehalis River Valley- Northern Hood Canal-Olympia and Southern Puget Sound- Shoreline / Lynnwood / South Everett Area-Southern Hood Canal. PZ...Small Craft Advisory until 5 AM PDT early this morning 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. && $$