458 FXUS66 KPDT 310607 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1007 PM PST Tue Dec 30 2025 .EVENING UPDATE...Opted to extend the Wind Advisory for Ladd and Pyles canyons through 3PM Wednesday since periods of advisory- level winds/gusts are still anticipated (80% confidence). Otherwise, the only update to the gridded forecast was to overnight low temperatures tonight and afternoon high temperatures for Wednesday. && .AVIATION...06Z TAFs...Predominantly VFR conditions are anticipated over the next 24 hours as a ridge of high pressure continues to dominate the weather. That said, some patchy low stratus is present along the Blue Mountain foothills south of PDT and northeast of ALW. Should this meander overhead or increase in coverage, LIFR to IFR CIGs/VSBYs will result; confidence in timing was too low (10-40%) to mention in the 06Z TAFs. Elsewhere, the 00Z HREF and 18Z REFS suggest very low (10% or less) probabilities of sub-VFR conditions. Winds will be light at 10 kts or less for all sites. && .PREV DISCUSSION... /issued 316 PM PST Tue Dec 30 2025/ DISCUSSION... Key Messages: 1. Breezy Grande Ronde Valley today. *Wind Advisory Active* 2. High pressure dominates through Wednesday. *Air Stagnation Advisories Active* 3. Precipitation returns Thursday, potential for freezing rain. Current radar and visible satellite imagery shows dry conditions and mostly clear skies, with some pockets of stratus along the base of the Blue Mountains and over North-Central Oregon. Surface high pressure is centered along the Idaho border, which is creating a slight pressure gradient over the Grande Ronde Valley. This has initiated breezy conditions early this morning, and is expected to persist through the evening as sustained winds of 25-35 mph and gusts of up to 55 mph will be possible. Maximum wind gusts of 50 mph have been observed at the Charles Reynolds Rest Area within the last hour. Thus, a Wind Advisory has been issued for the Grande Ronde Valley, specifically over the Ladd and Pyles Canyons until 11PM this evening. NAM and SREF guidance suggests that pressure gradients will temporarily slacken but increase through the early morning hours on Wednesday, so this advisory may need to be extended (40-50% chance). High pressure is also present in the mid-and upper levels of the atmosphere, as a ridge continues to slowly strengthen over the area before slowly weakening and shifting east on Wednesday. This has provided mostly clear skies and low winds across the Lower Columbia Basin as sinking air keeps temperatures about 5 degrees below normal for this time of year. Highs will peak in the mid-30s through Thursday as lows dip in to the low to mid-20s across the Columbia Basin. This lack of moving air will not only allow for the potential for developing pockets of freezing fog during the morning hours, but will promote the potential for degrading air quality. Currently, moderate (51-100 AQI) air quality is being observed across Central Oregon, North-Central Oregon, and the Yakima Valley, with this trend expected to continue through Thursday morning. As a result, an Air Stagnation Advisory is active through noon on Thursday. The upper level ridge continues to weaken and push to our east Thursday as an upper level low pressure drops into the Eastern Pacific from the Gulf of Alaska and approaches the coast. This will enhance southwest flow aloft and bring moisture into the region from the south. The resident cold air will still be present across the Columbia Basin, Gorge, Yakima/Kittitas Valley, and portions of Central Oregon as the moisture moves in Thursday morning. The weak frontal system that is bringing the moisture onshore along the California coast will break up before reaching southern Oregon, leading to the lack of synoptic forcings to properly scour the cold air from lower elevations of the aforementioned areas. This will set up the potential for freezing rain to occur, with current confidence of up to 0.10" of ice over lower elevations of the Columbia Basin (Hermiston & Tri-Cities) at 50-60%. The NBM is showing a vertical profile that would allude to freezing rain potential, with 850 mb temperatures of 34-41 degrees, 925 mb temperatures of around freezing, and surface temperatures between 25-30 degrees. LREF soundings advertise a deep warm nose of temperatures up to around 9000 feet, suggesting liquid precipitation with near surface temperatures well below freezing - especially in the early morning hours. 56% of ensembles confirm and slightly lean to even colder surface temperatures Thursday morning associated with a weaker and earlier trough, better aligning with cold overnight/early morning temperatures. These conditions may warrant the need for an advisory in the next 36 hours. 75 && .PRELIMINARY POINT TEMPS/POPS... PDT 21 36 22 34 / 0 0 0 20 ALW 24 34 25 34 / 0 0 0 20 PSC 23 38 22 34 / 0 0 0 10 YKM 25 39 22 35 / 0 0 0 10 HRI 22 37 23 34 / 0 0 0 10 ELN 16 34 19 34 / 0 0 0 10 RDM 23 44 24 44 / 0 0 10 30 LGD 30 44 29 43 / 0 0 0 30 GCD 29 48 29 45 / 0 0 10 50 DLS 26 40 27 37 / 0 0 0 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Air Stagnation Advisory until noon PST Thursday for ORZ044-507- 508-510-511. Wind Advisory until 3 PM PST Wednesday for ORZ049. WA...Air Stagnation Advisory until noon PST Thursday for WAZ026>029. && $$ EVENING UPDATE...86 DISCUSSION...75 AVIATION...86