FXUS66 KPQR 272148 AFDPQR Area Forecast Discussion National Weather Service Portland OR 248 PM PDT Tue Aug 27 2024 .SYNOPSIS...High pressure building into the region will bring a steady warming and drying trend through the holiday weekend, peaking on Saturday with highs in the mid 90s. Low pressure approaching from offshore will bring a chance of thunderstorms mainly along the Cascades on Sunday. Onshore flow and more seasonable temperatures return early next week. && .DISCUSSION...Visible satellite imagery reveals clearing skies across northwest Oregon and southwest Washington this afternoon as an upper level trough and an associated weak surface front depart east of the Cascades. A tightening onshore pressure gradient behind these features is making for a breezy afternoon across the area, with gusts of 20-25 mph gusts out of the north-northwest commonly being reported at many observation sites. Temperatures will begin a steady upward trajectory on Wednesday as high pressure builds over the region as highs climb back to around 80 through much of the interior lowlands. Light offshore flow will also develop on Wednesday and strengthen a bit Wednesday night into early Thursday morning, leading to some modest easterly winds on the mid and upper slopes of the Cascades as well as through the Columbia River Gorge. Still do not expect winds to be overly strong as the cross Cascade pressure gradient approximated by TTD-DLS only peaks around -4.5 mb early Thursday morning, translating to 20-25 mph gusts over over exposed higher slopes and perhaps slightly higher gusts through the Gorge. Expect these east winds to diminish by Thursday afternoon as hotter and drier conditions develop. Speaking of Thursday afternoon, high temperatures will jump up to around 90 across much of the interior as high pressure strengthens overhead and 850 mb temps climb to around +16 C. This will bring HeatRisk into the moderate category across the area, a trend that will continue into Friday as highs creep up into the low to mid 90s. Temperatures will peak on Saturday as 850 mb temps reach 24-26 C, corresponding to highs in the mid to perhaps upper 90s in a few spots. The probability to reach or exceed 95 degrees is generally in the 40-60 percent range across the Willamette Valley on Saturday afternoon. Meanwhile, the probability to reach 100 degrees is sitting at 10 percent or less lending a relatively high degree of confidence in the range of temperature outcomes likely sitting in the mid 90s. This results in a few pockets of major HeatRisk in and around the Portland metro area on Saturday, contributing to an elevated concern for heat related impacts as we begin the holiday weekend. The other forecast concern heading into the weekend will be thunderstorm potential as a cutoff upper low currently sitting over the open Pacific near 35N 140W gets dislodged and starts to approach the California or southern Oregon Coast. Thunderstorm potential for Saturday has waned a bit over our area as it looks like the upper low will remain far enough offshore and to the south to keep the best chances to the south through Saturday. Sunday looks to provide a better opportunity as the low moves closer to the coast and draws mid level moisture characterized by precipitable water values of 0.9-1.0" northward into the area. Models are still depicting slight differences in the low position from off of Cape Mendocino to closer to the Oregon border, which will have implications on how far north the thunderstorm threat extends. For now, area along the Cascades roughly south of Mt Hood look to have the best potential, carrying a 15 percent chance through Sunday evening. Given the increase in mid level moisture, would expect these storms to be accompanied by at least some rain. In terms of temperatures, highs should start to trend back down into the upper 80s by Sunday as the cutoff draws closer and shifts the ridge axis east to the Rockies. A larger cooldown then arrives next MOnday into Tuesday as the upper low weakens into an open wave and moves onshore, ushering in stronger onshore flow and returning temperatures closer to seasonal norms in the upper 70s to low 80s. /CB && .AVIATION...Widespread VFR conditions throughout the airspace. Expect these conditions to prevail through the TAF period, with the only exception of a 10-30% probability of MVFR CIGs developing between 12-17Z Wednesday for most terminals. Otherwise, there will be increased north/northwesterly winds today, with gusts up to 25 kt along the coast (highest at KONP) and some inland locations until 04Z Wednesday. PDX APPROACHES...Prevailing VFR conditions throughout the TAF period (other than a 20-30% chance of MVFR between 12-17Z Wednesday). Increased northwesterly winds with gusts up to 22 kt until 04Z Wednesday, decreasing thereafter. -Sala && .MARINE...High pressure begins to move into our waters and is expected to persist throughout this week, bringing increased northerly surface winds during afternoon hours. A Small Craft Advisory is in effect across the inner and outer waters south of Cape Falcon with up to 25 to 30 knots expected until early Thursday morning. It still appears winds will be a little too marginal to issue a Small Craft Advisory north of Cape Falcon but isolated gusts around 20-23 knots can't be ruled out (30-50% chance). Seas will remain between 6 to 8 feet throughout the week, briefly increasing up to 9 feet on Wednesday. NW swell of 5 to 7 feet with a 7 to 9 second period will persist through the weekend. -Sala && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 2 AM PDT Wednesday for PZZ252-253. Small Craft Advisory from 11 AM Wednesday to 6 AM PDT Thursday for PZZ252-253. Small Craft Advisory until 6 AM PDT Thursday for PZZ272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland