983 FXUS66 KPDT 281143 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 443 AM PDT Sun Sep 28 2025 .Updated Aviation Discussion. .AVIATION...12Z TAFS...VFR conditions currently across all sites, which will stay the course through the period. Light winds below 10 kts will persist, with KRDM/KBDN being the exception as winds will hover around 10 kts this afternoon. Cloud cover will increase in the evening as a system approaches from the west, with ceilings of 25kft. 75 && PREV DISCUSSION... /issued 341 AM PDT Sun Sep 28 2025/ DISCUSSION... Key Messages: 1. Warm and dry day ahead. 2. Showers and isolated thunderstorm threat through week. Current radar and infrared satellite imagery shows dry conditions as a thin veil of high level clouds slowly cross through the area. This is in response to the incumbent ridge slowly beginning to depart to our east as an upper level trough approaches the coast later today. Southwest flow aloft will enhance today to provide a slightly warmer day with highs peaking in the low to mid-80s across the Columbia Basin and lower elevations of Central Oregon. These values are about 10 degrees above normal for this time of year, which will also be coupled with afternoon humidities dipping down between 15-25%. Lower humidity values are expected to occur across the John Day Basin, Northern Blue Mountains/Foothills, Grande Ronde Valley, and lower elevations (<4500') of Wallowa County. Confidence in these areas experiencing humidities below 20% is high as the HREF suggests a 70-90% chance of occurrence. Winds will be slightly more elevated today as a pressure gradient develops along the Cascades. The NAM, SREF, and GFS all advertise a pressure gradient of 4.3-4.9 mb between Medford (MFR) and Pendleton (PDT), which corresponds to sustained winds of 10-15 mph with gusts up to 20 mph across Central Oregon. The HREF is in alignment with these winds, highlighting a 65-85% chance of winds reaching 15 mph or above and gusts of 20 mph or higher east of the La Pine/Bend area between 2-5 PM. Elevated winds of 10-15 mph with gusts of 20 mph are also expected through the Columbia Gorge, Simcoe Highlands, and the through the Cascade gaps west of Yakima as the GFS, NAM, and SREF also show a 3-3.5 mb pressure gradient developing between Portland (PDX) and Hermiston (HRI). Confidence in these winds is not as strong as across Central Oregon, with the NBM suggesting a 40-50% chance of sustained winds of 15 mph or greater with a 45-65% chance of gusts of 20 mph or greater. These winds will be occurring in areas of improved humidities from Saturday, leading to minimal fire weather concerns. Clouds will increase this evening and into Monday as rain chances (20-40%) begin to spill over the Cascade crest and extend into the eastern slopes. Showers become widespread by late afternoon and evening as the upper level trough moves onshore and the associated cold front slowly passes through the Columbia Basin into Tuesday morning. This trough is one of many that will be passing through the Pacific Northwest through the week, as a strong upper level low pressure system drops from the Gulf of Alaska Monday and approaches the coast later in the week. However, this first trough looks to be the most efficient at bringing widespread rain amounts across the region as it taps into subtropical moisture from the 25-30N latitudes. As a result, a wetting rain (=>0.10") is anticipated to occur through much of the area (40-60% chance via NBM) with the exception of the Tri-Cities area (24%) and Yakima (31%). The highest rain amounts of around 0.20" will occur over the John Day Highlands and the northern Blue Mountains with 50-60% confidence. Rain amounts Tuesday and Wednesday will struggle to reach wetting rain amounts outside of the Cascade crest, east slopes of the Cascades, Elkhorns, and higher elevations of the Blue Mountains. The incoming system will also bring with it the chance for isolated thunderstorms as it erodes the backside of the upper level ridge. The best chances will occur along the east slopes of the Oregon Cascades into the US-97 corridor and across Grant, Union, and Wallowa counties as the NAM advertises 100-200 J/kg of surface CAPE. The NAM also hints at this same amount of CAPE over Wallowa County on Tuesday afternoon, and the GFS shows 50-150 J/kg of CAPE across the Cascades, Columbia Basin, and the northern Blue Mountains/Foothills on Wednesday. At this time, Wednesday does look to have more of a widespread thunderstorm threat, however, models and ensembles are in disagreement on the timing and progression of the upper level low pressure as it moves onshore. Currently, ensemble members are split between the low opening up and moving inland along the British Columbia coast Wednesday or pushing onshore along the Oregon/California coasts late Thursday. Currently, the former scenario is the front-runner, which would lead to a better potential for isolated thunderstorms as additional CAPE would be available. Even with the potential for afternoon thunderstorms, they are expected to stay discrete and sub-severe (<10% chance of severe storms). 75 && .PRELIMINARY POINT TEMPS/POPS... PDT 83 53 78 53 / 0 10 20 60 ALW 83 58 79 58 / 0 10 10 60 PSC 83 53 78 54 / 0 0 10 50 YKM 82 55 76 51 / 0 10 20 50 HRI 83 54 79 54 / 0 10 20 50 ELN 80 51 73 48 / 0 20 30 60 RDM 84 49 73 42 / 0 10 40 60 LGD 86 53 77 52 / 0 10 20 80 GCD 86 52 75 48 / 0 10 40 80 DLS 84 59 76 55 / 0 10 40 60 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...75 LONG TERM....75 AVIATION...75