Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
567 FXUS66 KSEW 080920 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 220 AM PDT Mon Jul 8 2024 .SYNOPSIS...Unseasonably hot conditions will continue through the first half of the week under a strong upper level ridge. Some relief is expected mid-week as the ridge pivots eastward and weekend, though above normal temperatures and dry conditions will persist through the forecast period. * HEAT...Warming will continue through Tuesday, with temperatures nearing or surpassing daily records across much of the lowlands apart from the coast. A Heat Advisory remains in effect for the entire region, ending Tuesday morning along the coast and Tuesday evening elsewhere. * FIRE WEATHER...Dry, hot, and unstable conditions have led to a Red Flag Warning for the Cascades through Tuesday evening. Fuels across the area continue to dry out rapidly, raising fire weather concerns for much of the region. && .SHORT TERM /TODAY THROUGH WEDNESDAY/...Hot and dry conditions will continue to intensify across western Washington to start the week as a strong high pressure ridge remains firmly in place over the southwestern US. High temperatures will increase a few degrees today and again into tomorrow, with areas of Moderate (orange) to Major (red) HeatRisk for much of the region apart from the coast. Overnight low temperatures will also remain elevated in the mid 60s for much of the lowlands, providing little relief from the hot daytime temperatures. The upper ridge axis will slowly push eastward through Tuesday, allowing for weak onshore winds to develop along the coast. However, a thermal trough building overhead will keep inland areas hot with little in the way of surface winds to cool things off. Warming will continue today and again into Tuesday, allowing temperatures to peak roughly 15-20 degrees above normal with much of the region seeing highs in the mid 90s. Additionally, a strengthening subsidence inversion over the mountains will maintain warmer conditions over the Cascades. Despite clear skies, temperatures Tuesday morning will stay well above normal in the mid 60s and providing a warm starting point for even warmer temperatures Tuesday afternoon. Temperatures are on track to continue to increase throughout the day Tuesday for inland areas, which will be the hottest day of the period, peaking in the upper 90s for most lowlands surrounding the Puget Sound. Areas southeast of the Sound will also see a moderate chance (30% to 40% probability) of temperatures reaching 100 degrees. Several daily high temperature records will likely be broken Tuesday. However, areas along the coast will see a different story as onshore flow continues to develop as the ridge shifts eastward, allowing temperatures along the shores to begin to moderate. Some uncertainty remains over how strong the onshore flow will be once it develops, and areas as far as Chehalis, Olympia, and Shelton may see some moderation in temperatures by early Wednesday morning. Forecast models show good agreement over conditions finally beginning to cool down on Wednesday as a weak shortwave brings onshore flow further inland. Inland areas will see highs in the upper 80s, still roughly 10-15 degrees above normal, but enough for HeatRisk to decrease into the Minor (yellow) category for most areas outside of the Seattle/Tacoma metro areas. Areas of urban heat stress may persist on Wednesday, especially after another night of elevated temperatures, and the need for heat related headlines continues to be monitored for areas from Seattle east into the Cascade valleys. .LONG TERM /THURSDAY THROUGH SUNDAY/...Warm temperatures are favored to continue through the rest of the week as western Washington remains on the periphery of a strong ridge drifting eastward over the southern US. While light onshore flow will keep the coast in the low 70s, areas inland will see highs in the low to mid 80s through the period. Ensembles also remain in good agreement over dry conditions through the week, with virtually no signal of incoming precipitation. Lindeman && .AVIATION...A strong upper ridge remains in place over Western Washington with light west to northwest flow aloft. Clear skies will prevail apart from a very shallow marine layer along the immediate coast which may produce some tempo LIFR/IFR conditions at KHQM this morning. KSEA...Clear skies. Surface winds N/NE 5 to 10 knots backing to NW this afternoon. 27 && .MARINE...Thermally induced low pressure remains in place across the interior of Western Washington with broad surface ridging over the coastal and offshore waters. Onshore flow is light. By midweek, the surface ridge offshore will strengthen and the thermal trough will shift east of the Cascades in response to a weak weather system passing well north of the area. This will lead to an increase in onshore flow by Tuesday night into Wednesday. Small craft advisory westerlies are expected in the central/east strait by Tuesday evening with possible gales Wednesday afternoon/evening. Small craft advisory conditions are also expected for the second half of the week over the outer coastal waters with the expected increase in onshore flow. 27 && .FIRE WEATHER...Strong high pressure will continue to bring very warm and dry conditions to the region. Instability over the Cascades will allow the Red Flag Warning for the Cascade Zones (658 and 659) to continue unchanged. Elsewhere, critical afternoon relative humidities will persist for the lower elevations and foothills south and east of the Puget Sound, but uncertainty remains over fuel readiness and instability paired with relatively calm winds and the threat for critical fire weather conditions will continue to be monitored for these areas. Onshore flow will bring somewhat higher humidities for the coastal and Olympics zones Monday, but it could be as late as Wednesday before portions of the Cascades see notable improvement. 15 && .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 11 AM PDT Tuesday for Central Coast-North Coast-Western Strait of Juan De Fuca. Red Flag Warning until 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. && $$