FXUS66 KPQR 062300 AFDPQR Area Forecast Discussion National Weather Service Portland OR 400 PM PDT Fri Sep 6 2024 .SYNOPSIS...Hot and dry conditions through tomorrow, with a 15-20% chance of thunderstorms over the Linn and Lane County Cascades this afternoon/evening. Expect hazy skies to continue through tomorrow as weak offshore winds push wildfire smoke west of the Cascades. Elevated fire weather concerns continue for the Cascades through tomorrow evening for dry and unstable conditions. More seasonable conditions with cooler temps and chances for rain begins next week. && .SHORT TERM...Now through Sunday night...Unseasonably hot temperatures expected through tomorrow, with the hottest temps this afternoon. As of 245 PM PDT, interior locations have reached the upper 80s to low 90s so far. Expect highs later this afternoon to peak in the mid to upper 90s. Reaching the triple digits looks less likely due to smoke aloft, which is limiting surface heating. As the thermal trough sits over the Willamette Valley, this has been resulting in light easterly winds. This offshore flow has been helping push smoke from ongoing wildfires west of the Cascades. As pressure gradients ease through this evening, winds will also weaken, but hazy skies are expected to continue through tomorrow. Also this afternoon and evening, an upper level trough approaching the area will lead to a slight chance (15-20%) of isolated showers across northwest OR and southwest WA. In addition, the Linn/Lane County Cascades and parts of the southern Willamette Valley east of I-5 have a 10-20% chance of isolated thunderstorms. Most of these showers and thunderstorms will be elevated, and the dry low levels will make it very difficult for precipitation to reach the surface. Radar imagery as of 3 PM PDT already shows altocumulus clouds rolling into the southern portion of our CWA as well as thunderstorms near south central Oregon. With southeast steering flow, convective debris could spill over into our area. Will note that there is low confidence for any abundant thunderstorm activity in our area. Expect overnight lows to remain rather warm, especially for urban areas, the Columbia River Gorge, and the Cascade foothills and valleys. These locations could struggle to fall below 65 to 70 degrees, limiting overnight relief from the heat. However, onshore flow will allow the coast and the southern Willamette Valley to have cooler overnight temps in the mid to upper 50s. This weekend, conditions will begin to cool down (relatively speaking) into the upper 80s to low 90s for interior locations. The aforementioned thermal trough will move eastward tomorrow over the Cascade crest as the upper level trough pushes through, returning onshore flow. Expect this gradual cooling trend to continue into early next week. -Alviz && .LONG TERM...Monday to Thursday...Upper ridge will be east of the Cascades on Monday, with onshore flow across western Oregon/Washington. As such, will maintain weather more typical for early September, with highs in the 60s along the coast, and 70s to lower 80s across the interior. Upper trough will be approaching the region on Tuesday, with uptick of the onshore flow. As such, will have more in the way of marine clouds in the morning, otherwise, increasing clouds as the day progresses. Does appear any precipitation will remain offshore during the day. Bit cooler, with 60s on the coast, and lower to middle 70s inland. ECMWF and GFS models in fairly good agreement in bringing that trough inland Tuesday night and Wednesday. As such, will see areas of precipitation spreading inland Tuesday night into early Wednesday, then showers later Wednesday into Wednesday night. While most areas will get some precipitation, still quite a bit of uncertainty as to how much. But, definitely looks to be plenty of clouds and cooler weather for Wednesday, with highs over much of the region in the 60s (50s in the higher terrain). Afterwards, high pressure will build back across the region, with mid-September like conditions for Thursday and Friday. /Rockey && .AVIATION...Warm air mass remain in place, with southerly flow aloft. Will maintain mix of mid/high clouds into this evening, along with a small chance of few showers or thunderstorm mainly south of a KTMK to KSLE to Mt Jefferson line through tonight. Otherwise will remain VFR and dry, with variable slant- wise visibility due to haze and smoke, especially over the Cascades. Will maintain widespread stratus and fog along the coast today and tonight, mainly on the beaches and offshore. But, low clouds and fog will surge back onshore this evening. Onshore flow will pick up the Coast Range gaps later tonight, and may be enough to bring some IFR to low MVFR clouds up the Siuslaw gap to be around KEUG late tonight into early Sat am. PDX APPROACHES...VFR with variable mid/high clouds today. Winds remain light. Main issue will be variable slant-wise visibility due to haze/smoke aloft, especially over the Cascades. /Rockey && .MARINE...Thermal trough sit inland, with high pressure offshore. Pressure gradients strong enough to support gusts to 20 to 25 kt over the outer coastal waters into tonight. Otherwise, will maintain little chance in the pattern, with north to northwest winds 10 to 15 kt and afternoon/evening gusts 15 to 20 kt. Will maintain current Small Craft Advisory for that overnight. Seas staying mostly at 4 to 6 ft through the weekend. && .FIRE WEATHER...Mesoanalysis as of 330 PM PDT shows a weak thermal trough sitting over the Willamette Valley, which is bringing weak offshore flow. Models are suggesting KTTD-KDLS pressure gradients will continue to ease, resulting in weakening winds through this evening. Therefore, the Red Flag Warning for dry and windy conditions in the the Columbia River Gorge (zone 636) is set to expire at 11 PM PDT this evening. Meanwhile, even though winds are also weakening over the Cascades, we'll still have unstable conditions through tomorrow. As the aforementioned thermal trough moves east over the Cascade crest, unstable conditions may be favorable for rapid fire spread. Model soundings are also showing a well-mixed layer above 6000 ft. Combined with forecast min RHs of 15-25% in the Cascades tomorrow, went ahead and extended the Red Flag Warnings for all Cascade zones (634, 635, 688, 689, 690) through 8 PM Saturday. Note that there is also a 15-20% chance of isolated thunderstorms over the Willamette National Forest this afternoon and evening. Any storms that form may produce lightning and gusty erratic outflow winds. However, since confidence is low for abundant lightning, it was not mentioned as the main headline in the Red Flag Warning. -Alviz && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Heat Advisory until 10 PM PDT this evening for ORZ104>107. Excessive Heat Warning until 10 PM PDT this evening for ORZ108>128. WA...Heat Advisory until 10 PM PDT this evening for WAZ202-203. Excessive Heat Warning until 10 PM PDT this evening for WAZ204>211. PZ...Small Craft Advisory until 5 AM PDT Saturday for PZZ271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland