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Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
430 FXUS66 KSEW 060340 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 840 PM PDT Fri Jul 5 2024 .SYNOPSIS...Very warm temperatures into next week for Western Washington as an upper level ridge slowly drifts over the area. Temperatures will peak Sunday through Tuesday with highs over the interior in the mid 80s to near 100. The ridge will slowly exit to the east making for a gradual cooling trend in the middle of next week. Key Messages: * HEAT...Continued warming will lead to hot conditions into next week. Temperatures will peak Monday and into Tuesday for the interior in the upper 80s to near 100. Highs will be cooler along the coast. A Heat Advisory is in effect for the entire region, ending Sunday evening for the coast, and Tuesday evening elsewhere. * FIRE WEATHER...Increasing dry and unstable conditions for this weekend has warranted the issuance of a Red Flag Warning for the Cascades through Tuesday. See the Fire Weather discussion below for details. && .SHORT TERM /TONIGHT THROUGH TUESDAY/...No significant changes to the forecast this evening. Temperatures topped out in the low to mid 80s through most of the interior near and north of Seattle as well as the Pacific Coast, with low 90s observed throughout the Southwest Interior and the Cascade valleys. Temperatures as of 8PM have began to sink into the upper 70s to upper 80s. Lows remain on track tomorrow morning for the mid to upper 50s tonight, with low to mid 60s expected in the Seattle urban core. LH From Previous Discussion...The upper ridge will continue to build over the Pacific Northwest through the weekend and into Monday with hot temperatures and dry conditions. Temperatures will generally increase a few degrees Saturday and again on Sunday. Highs both days will be in the 80s to mid 90s, with the hottest temperatures generally King County southward, in the Chehalis Valley, and into the slopes of the Cascades and Olympics. In addition, overnight temperatures will remain elevated, with little overnight relief, with lows in the upper 50s to mid 60s. Temperatures will be slightly cooler along the immediate coast this weekend, with highs in the upper 70s to low 80s, although a sharp gradient will be likely moving inland. The ridge axis will move over western Washington Monday into early next week, with likely the warmest days for the interior Monday and Tuesday. Highs Monday will range in the mid 80s to 90s, although perhaps a few 100 degree marks will be possible in the Cascade Valleys as well as Lewis and Mason Counties. Overnight temperatures will continued to remain elevated as well, although cooler temperatures are expected along the coast due to slight increase in onshore flow. HeatRisk will be widespread Moderate to areas of Major through early next week, with heat impacting most individuals sensitive to heat, especially though without effective cooling or adequate hydration. Make sure to stay hydrated during this period. .LONG TERM /WEDNESDAY THROUGH SATURDAY/...The ridge axis generally remains over western Washington on Tuesday, although another slight increase in onshore flow is expected for the coast. Hot conditions will continue, especially for the interior, with the Heat Advisory extended through Tuesday for interior areas. Ensembles suggest the ridge axis slowly slides east on Wednesday as a weak shortwave slides north of the area into Thursday. However, continued ridging influence will lead to well above normal temperatures, despite an increase in onshore flow. NBM suggests highs remain in the 80s to near 90 for the interior, with further cooling into Thursday. Above normal temperatures and dry weather likely to continue late next week. JD && .AVIATION...Northwesterly flow aloft as high pressure amplifies over the west. Dry and stable airmass over the region will continue to lead to VFR conditions at all sites throughout the TAF period. KSEA...VFR persisting thru the TAF period. North winds this evening still hanging around 10 to 15 knots, but by 06Z will turn more NE this evening with speeds decreasing to around 4 to 8 knots. Maz/18 && .MARINE...Expanding thermal trough along the trough will give way to periods of light offshore flow throughout the weekend. Recent guidance suggests flow turning slightly more onshore Monday night into Tuesday, with stronger pushes down the Strait of Juan De Fuca likely into midweek. Coastal seas generally 4 to 6 feet into the weekend and through early next week. Maz/18 && .FIRE WEATHER...All remains consistent in regards to the amplification of a stout upper-level ridge over the PNW. Hot temperatures, dry conditions, and slight instability all falling upon the holiday weekend has lead to the issuance of a fire weather watch beginning Saturday afternoon for Cascade zones 658 and 659 Fortunately, there`s no wind to combat with as a thermal trough remains far to the south over S OR. However, this prolonged heat event will dry out fuels rapidly. Critical RH values are likely over the Cascades with isolated areas within the Olympic Mountain valleys over the weekend. Model trends continue to push back the improving fire weather conditions into now Tuesday- Wednesday. Decent RH recoveries won`t arrive to the Olympic and coastal zones until then, however, the interior may not feel relief until late next week. McMillian && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Heat Advisory until 10 PM PDT Tuesday for Admiralty Inlet Area- Bellevue and Vicinity-Bremerton and Vicinity-East Puget Sound Lowlands-Eastern Strait of Juan de Fuca-Everett and Vicinity-Hood Canal Area-Lower Chehalis Valley Area- Olympics-San Juan County-Seattle and Vicinity-Southwest Interior-Tacoma Area-West Slopes North Cascades and Passes- West Slopes North Central Cascades and Passes-West Slopes South Central Cascades and Passes-Western Skagit County- Western Whatcom County. Heat Advisory until 10 PM PDT Sunday for Central Coast-North Coast-Western Strait of Juan De Fuca. Red Flag Warning from 11 AM Saturday to 11 PM PDT Tuesday for West Slopes of the Central Cascades Generally above 1500 Feet-West Slopes of the North Cascades Generally above 1500 Feet. PZ...None. && $$