324 FXUS66 KPDT 302316 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 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 && .AVIATION...00Z TAFs...A patch of LIFR stratus developed late This Morning in the vicinity of PSC/ALW which complicated an otherwise VFR setup across all terminals. With high pressure pattern remaining in place, this risk of ceilings could return overnight, although confidence is not high, model ensembles are producing better areal coverage of the low probability (20-30%) risk for 1/2SM vsby and LIFR cigs after about 6z for ALW/PDT. Light winds under 5 knots is anticipated at all terminals. Russell/71 && .PRELIMINARY POINT TEMPS/POPS... PDT 22 36 22 34 / 0 0 0 20 ALW 25 34 25 34 / 0 0 0 20 PSC 25 34 22 34 / 0 0 0 10 YKM 23 37 22 35 / 0 0 0 10 HRI 24 34 23 34 / 0 0 0 10 ELN 20 34 19 34 / 0 0 0 10 RDM 25 49 24 44 / 0 0 10 30 LGD 30 43 29 43 / 0 0 0 30 GCD 30 48 29 45 / 0 0 10 50 DLS 27 38 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 11 PM PST this evening for ORZ049. WA...Air Stagnation Advisory until noon PST Thursday for WAZ026>029. && $$ DISCUSSION...75 AVIATION...71