Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
348 FXUS66 KPDT 182047 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 147 PM PDT Mon Aug 18 2025 .DISCUSSION...Today through Sunday night... Key Messages: 1. Breezy winds through Cascade gaps and Kittitas Valley. 2. Warming and drying trend Wednesday onward, peaking Saturday. Current radar and visible satellite imagery showing dry conditions under mostly sunny skies. This is in response to the upper level ridge slowly building in from the southeast as an offshore upper level low pressure system begins its onshore push into British Columbia. This low pressure system will move onshore into Tuesday morning, continuing to ride over the present ridge located over the Four Corners area. The synoptic pattern will promote elevated winds across the Kittitas Valley and the Columbia Gorge as a surface pressure gradient develops across the Cascades during the afternoon both Tuesday and Wednesday. Sustained winds of 10-20 mph with gusts up to 30-35 mph will be possible, peaking Wednesday afternoon as additional upper level support is achieved with a passing embedded shortwave. Confidence in these wind values is high (70-80%) as the NBM suggests a 75-95% chance of sustained winds reaching 20 mph or greater and a 60-80% chance of 35 mph gusts, primarily on Wednesday. Temperatures during this timeframe stay seasonal, with highs in the mid-80s to low 90s and lows dropping into the low 50s to low 60s. The present southwest flow aloft also keeps afternoon humidities above critical values in the upper teens to low 30s with moderate to good (50-70%) overnight recoveries expected through Thursday morning. There is an outside chance (<15%) of an isolated thunderstorm across the Eastern Mountains Tuesday and Wednesday, but recent guidance continues to trend downward on this potential threat. This is due to the lack of moisture at mid-levels, which is a result from the encroaching upper level ridge to our southeast. The best chance of afternoon thunderstorms will be experienced across Wallowa County. The upper level low pressure continues on its Canadian tour, moving into Alberta Wednesday morning and Saskatchewan on Thursday to allow a transient ridge to align with the one building over the Four Corners area and strengthen across the Pacific Northwest. This feature will lead to significant warming and drying Friday onward. A slight uptick will be experienced on Thursday, but will be more of a transition day as flow aloft will shift from the southwest to the west. The ridge axis will be over the area Friday before shifting to our east and stalling over the weekend. High temperatures will break into the upper 90s across the Basin Friday before pushing into the low triple-digits both Saturday and Sunday, which is about 10 degrees above normal. Little overnight relief is expected Saturday and Sunday mornings as lows will only drop into the mid-60s to low 70s across the Basin and Central Oregon. These temperatures may lead to heat highlights being issued over the weekend with areas of Major HeatRisk developing both Saturday and Sunday. Humidities will begin to degrade Thursday morning as moderate recoveries (35-50%) are anticipated across the region, with the lowest amounts along the east slopes of the Washington Cascades and the Yakima/Kittitas Valleys. Afternoon humidities will hover in the teens across the region, with areas of Central Oregon pushing into the upper single digits Friday and Saturday. Due to the present upper level ridge, winds look to be on the low end. However, there are some areas of concern for OR zones 696 and 703 Friday and Sunday as gap winds may contribute to critical fire weather conditions. This will be analyzed further as the event nears. 75 && .AVIATION...18Z TAFS...VFR conditions currently across all sites, which will stay the course through the period. Breezy winds for KDLS/KPDT/KRDM/KBDN through the afternoon with gusts of 15-25 kts. Highest winds expected at KDLS. Clouds will dissipate through the afternoon and evening. 75 && .PRELIMINARY POINT TEMPS/POPS... PDT 56 87 58 87 / 0 0 0 0 ALW 61 89 62 87 / 0 0 0 0 PSC 59 91 59 90 / 0 0 0 0 YKM 56 89 59 88 / 0 0 0 0 HRI 59 90 61 89 / 0 0 0 0 ELN 54 84 57 82 / 0 0 0 0 RDM 46 86 47 85 / 0 0 0 0 LGD 53 90 54 86 / 0 0 10 0 GCD 51 91 52 87 / 0 0 0 0 DLS 59 86 62 87 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...75 LONG TERM....75 AVIATION...75