138 FXUS66 KPQR 071015 AFDPQR Area Forecast Discussion National Weather Service Portland OR 315 AM PDT Thu Aug 7 2025 .SYNOPSIS...Seasonably cool temperatures continue today while lingering rain showers dwindle this afternoon. A marked pattern shift will see robust ridging develop offshore, bringing a warming trend through early next week. Heat is expected to reach hazardous levels Sunday and Monday, before cooling midweek. && .DISCUSSION...Now through Wednesday...An upper-level low apparent on satellite imagery over Vancouver Island will continue to track eastward along the Canada-US border through the end of the week. Its associated cold pool aloft will keep temperatures some 5-10 degrees below normal today. A few isolated to scattered rain showers remain possible as the low makes its nearest approach through this afternoon, but chances remain low, only 15-25% this morning and less than 15% this afternoon, with the highest likelihood along the coast and the western slopes of the Cascades. Starting on Friday, a major pattern shift will see robust upper-level ridging and surface high pressure begin to build over the northeast Pacific. As heights aloft rise overhead, surface temperatures will steadily warm through early next week. While unseasonably warm temperatures should be expected along the coast and in areas of high terrain by Sunday and Monday, the heat will reach hazardous levels within inland valleys. Afternoon high temperatures will very likely exceed 90 degrees along the Willamette Valley and Columbia Gorge, and in the Portland/Vancouver metro: 75-95% chances on Sunday and 85-100% on Monday, with higher likelihoods to the south. Slightly lower chances extend into the Lower Columbia and Cowlitz Valleys, 60-85% on Sunday and 75-90% on Monday. Some locales may also record their first triple digit temperatures of the year: chances to exceed 100 degrees are 10-25% on Sunday and 25-45% on Monday in the Portland/Vancouver metro and Columbia Gorge, 40-60% on Sunday and 65-85% on Monday in the Willamette Valley, and less than 15% on Sunday and 15-35% on Monday in the Lower Columbia and Cowlitz Valleys. Dewpoints in the low to mid 60s will additionally make conditions feel noticeably humid each afternoon. Temperatures will also be very mild on Sunday night, generally in the low to mid 60s, and similar or a few degrees cooler on Monday night. The combination of hot daytime temperatures and lack of sufficient overnight cooling can raise the cumulative heat stress and elevate the risk for heat illness, resulting in areas of Major HeatRisk most prevalent across inland valleys. An Extreme Heat Watch has therefore been issued from noon Sunday through 8 PM Monday throughout the Portland/Vancouver metro, Columbia Gorge and Lower Hood River Valley, Lower Columbia and Cowlitz Valleys, and the Willamette Valley. All residents, but especially those without access to adequate cooling or hydration, should make plans for this period of hazardous heat. By Tuesday and Wednesday, long-range ensemble solutions begin to diverge quite a bit. In the mean, the pattern deamplifies and shifts west away from the region as upper-level troughing develops over the Pacific Northwest, allowing temperatures to ease cooler back toward more seasonal values. The amplitude of potential troughing remains very uncertain, and some members instead maintain upper-level ridging, which could prolong heat impacts through more of the workweek. -Picard && .AVIATION...Currently as of 10Z Thursday, stratus lingers throughout the airspace, continuing to bring moments of deteriorated conditions at most terminals. Looking ahead, inland terminals will stay mostly VFR through the TAF period, with the exception being a low chance (20-30% chance) of MVFR conditions until 17-18Z Thursday. Breaks in stratus could lead to fog/mist development at some locations, as observed at KHIO with IFR/LIFR conditions. Confidence is low on exactly when and where foggy/misty conditions may develop, but any formation of such conditions will likely be brief. Along the coast, conditions differ from KAST to KONP, with MVFR/VFR conditions at KAST and LIFR conditions at KONP. Guidance suggests deteriorated conditions to persist until around 18-19Z Thursday, with a 40-60% chance for MVFR CIGs at KAST, and a 40-60% chance for LIFR conditions at KONP. Conditions should improve to VFR thereafter, but there is a 20-40% chance that coastal terminals will see a return of MVFR conditions after 00Z Friday. Otherwise, expect northwesterly winds through the period. Inland will see winds generally under 10 kt and coastal terminals will see winds around 10-14 kt with gusts up to 20 kt during the afternoon. PDX AND APPROACHES...Mostly VFR through the period, with a low chance (20-30%) of CIGs lowering to MVFR before 18Z Thursday. Thereafter, VFR conditions and northwesterly winds under 10 kt. ~Hall && .MARINE...Seas will stay around 6 ft at 10 seconds through at least Friday as a result of a passing front yesterday. Winds will remain elevated around 10 to 15 kt with gusts up to 20 kt, mostly in the southern waters today into Friday afternoon. Friday night and through the weekend, a ridge will build with a northerly wind reversal and conditions will take on a typical summer pattern. As temperatures warm considerably through the weekend, expects winds to ramp up throughout all the waters, with combined seas being dominated by wind wave. Moderate to high probability of Small Craft Advisory conditions in the southern waters starting Friday afternoon, then a high probability of Small Craft conditions in all waters by Saturday afternoon. ~Hall/Muessle && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Extreme Heat Watch from Sunday afternoon through Monday evening for ORZ108>118-120>122. WA...Extreme Heat Watch from Sunday afternoon through Monday evening for WAZ204>207-209-210. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland