FXUS66 KPQR 080930 AFDPQR Area Forecast Discussion National Weather Service Portland OR 230 AM PDT Thu Aug 8 2024 .SYNOPSIS...Hot, dry, and hazy/smoky conditions continue through Friday, with the hottest and smokiest conditions expected today. Increasing offshore flow will push smoke from ongoing wildfires westward into the Willamette Valley and Coast Range, impacting air quality. Onshore flow will keep conditions mild along the coast. A cooling trend is forecast this weekend into next week, with increasing morning clouds and chances for light rain or drizzle near or along the coast. && .SHORT TERM...Now through Friday night...Today is forecast to be another hazy and hot day as increasing offshore flow pushes wildfire smoke westward across northwest Oregon and southwest Washington. A weak thermal trough will set up today, which is what will lead to these weak offshore winds. How far west the east winds get will ultimately depend on how far west the thermal trough axis is set up. If the thermal trough is set-up over the Cascade crest, offshore flow may struggle to make it west of the crest. For more detailed info about the winds, see the fire weather section. Smoke is coming from wildfires burning in various locations across the region, especially the ongoing fires eastern Lane County, the Whiskey Creek Fire in the Gorge, and the Williams Mine Fire near Mt. Adams. Locations that are experiencing smoke at the surface and/or increasing ozone pollution will be dealing with periods of degraded air quality over the next 36-48 hours; thus, a variety of Air Quality Advisories remain in effect for parts of the Willamette Valley, Columbia River Gorge, southwest Washington lowlands, and the Cascades. Aside from air quality concerns, smoke is also impacting the temperature forecast. While the NBM typically performs quite well for temperatures this time of year, this is not the case when significant smoke and haze are a factor as the NBM does not directly account for the impact of smoke on temperatures. As such, the NBM typically runs too warm on days with wildfire smoke, assuming smoke layers aloft and/or near the surface are dense enough. This proved true in some locations yesterday, which observed high temperatures around 2 to 4 degrees cooler than what the deterministic NBM was suggesting. Given the fact that wildfire smoke will be increasing both aloft and near the surface today, we suspect that the deterministic NBM will be too warm again. As such, went ahead a nudged today's high temperatures forecast toward the NBM 10th percentile to bring it down a few degrees. Afternoon highs for interior valleys are now forecast to peak between 90 to 95 degrees F, rather than 95 to 100 degrees which was forecast earlier this week. As a result, this lowered the HeatRisk category for the Portland/Vancouver Metro Area today from "Major" HeatRisk to "Moderate" HeatRisk. Still hot, but not quite as hot as initially expected. Meanwhile, onshore flow will keep conditions mild at the coast as offshore flow is not expected to make it that far west. The flow regime turns back onshore on Friday, but could still experience some brief offshore winds in the morning in the Upper Hood River Valley and Cascade crest. We'll begin to see some improving air quality for areas west of the Cascades in the evening as westerly winds pick up. Places immediately downwind of current fires would likely continue to experience smoke and haze impacts. Temperatures will also begin to gradually cool each day, falling from the upper 80s/low 90s on Friday to the mid/upper 80s on Saturday. In addition, light rain or drizzle is possible along the central Oregon coast Friday into Friday night (15-30% chance) as a passing upper level shortwave helps deepen the marine layer. -Alviz/TK && .LONG TERM...Saturday through Wednesday...WPC cluster analyses are in agreement for weak upper level troughing over the Pacific Northwest this weekend. We'll likely remain warm and dry as the majority of ensemble members suggest 500 mb heights will be near average, but excessive heat is unlikely. NBM probability of 95 degrees or hotter this weekend in the Willamette Valley is only at 5-25%. The most likely outcome for high temps this weekend is mid to upper 80s for inland valleys and mid 60s to low 70s at the coast. There is also a 20-35% chance of light rain/drizzle near the coast Saturday night into Sunday morning as the marine layer will likely be deep enough. The western slopes of the coastal mountains will also have a 10-15% chance of light rain/drizzle given the light upslope winds. Monday to Wednesday, the majority of ensemble members still suggest broad troughing over the Pacific Northwest with relatively stronger onshore flow. 20% of members now show 500 mb heights falling slightly below average, while the remaining 80% show near normal heights. This would lead to a cool-down to average or slightly below average temperatures. Therefore, the current forecast calls for high temperatures in the upper 70s to low 80s for interior valleys early next week. Any meaningful precipitation with this trough still looks unlikely, but there is a 10-20% chance of 48 hour QPF amounts greater than 0.05 inch across northwest Oregon and southwest Washington (ending 5 AM Wednesday). At the very least, would suspect increasing chances for coastal drizzle with this type of pattern in place along with morning cloud cover for inland valleys. -Alviz/TK && .FIRE WEATHER...Today...Easterly winds will develop over the Columbia River Gorge and portions of the Mt. Hood and Gifford Pinchot National Forests (strongest along exposed ridges and east-west oriented valleys) today, resulting in near-critical fire weather conditions through the afternoon. Expect sustained winds between 5-15 mph with gusts to 20-25 mph. There is a low (20%) chance that exposed ridges prone to easterly winds could experience gusts as high as 30-35 mph. These winds will be occurring simultaneously with critical relative humidity values in the 15-20% range. While Red Flag Warning criteria will most likely not be met across most of our Columbia River Gorge fire zone, criteria may be met in localized areas for a few hours (e.g. exposed ridges prone to east winds). Although criteria is not being met across a large enough area to pull the trigger on a Red Flag Warning, conditions will still be favorable for an increase in fire activity and smoke production. Fortunately, east winds look to be short-lived, weakening in strength Thursday night into Friday morning before returning onshore Friday afternoon. -Alviz/TK && .AVIATION...West to southwest flow aloft as area remains under zonal flow today. Predominately VFR, except along the coast where marine stratus remains entrenched in LIFR CIGs (200-300 ft). Light onshore flow likely maintains these conditions along the coast until around 18Z this morning, though KONP may see these conditions persist through the TAF period. Expect north to northwest winds increasing to around 10 kt in the afternoon and evening. Smoke from wildfires burning across the region could result in some slant range visibility issues. PDX AND APPROACHES...VFR conditions expected with mostly clear skies, though smoke from nearby wildfires will likely produce hazy skies through this afternoon. Surface winds expected to remain northwest 3-5 kt this morning, increasing up to 10 kt this afternoon. /DH && .MARINE...High pressure anchored offshore will result in persistent north to northwest winds across the coastal waters through the weekend. Winds currently gusting to 20-25 kt early this morning are expected to gradually ease below 20 kt today. Will likely allow the Small Craft Advisory to expire at 5 AM this morning. Seas around 4 to 7 ft this morning subside to 3 to 5 ft as winds ease. Seas will be primarily wind driven through the weekend. /DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 5 AM PDT early this morning for PZZ272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland