Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
509 FXUS66 KPDT 181741 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1041 AM PDT Mon Aug 18 2025 .Updated Aviation Discussion. .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 && PREV DISCUSSION... /issued 142 PM PDT Sun Aug 17 2025/ DISCUSSION...Satellite imagery this afternoon shows fairly sparse cumulus fields developing over the higher terrain of the OR Cascades and the eastern mountains. Otherwise, skies are mostly clear with a band of cirrus passing over central WA. Today through Monday: The PacNW will continue to sit under the influence of a broad upper low in the northeast Pacific, keeping temperatures near normal. Shortwave impulses swinging around the bottom of this low will move across the forecast area later this afternoon and overnight, initiating shower and thunderstorm activity mainly across the eastern mountains, with an isolated cell or two developing in central OR. Some CAMs members and the deterministic NAM and ECMWF indicate another impulse passage late tonight into early tomorrow morning, resulting in shower chances (15-20%) developing across portions of the eastern mountains into the Columbia Basin and eastern portions of the Yakima Valley. Upper level ridging will begin to build northwest into the PacNW Monday, greatly decreasing chances of shower activity across the forecast area. That said, a slight chance (~10-15%) of isolated thunderstorms will be possible across portions of Wallowa and Union counties in the afternoon. Otherwise, the area will start to see some warming, though temperatures will be near to below normal. Tuesday through Saturday: High confidence (75-90%) in upper level ridging continuing to build into the region Tuesday with a warming and drying trend that will persist throughout the week. Wednesday, ensemble cluster solutions are in fairly good agreement that a dry shortwave will flatten the ridge briefly, with locally breezy winds developing through the Cascade gaps as the main threat. However, 12Z deterministic guidance and the ECMWF ensemble mean indicate a slight chance (~15%) for isolated thunderstorms to develop across the Blues and Wallowas as the shortwave reaches this area. Confidence is currently low (10-20%) in occurrence, so have left out of the afternoon forecast package at this time. After Wednesday, ensemble cluster members stay in great agreement that upper level ridging over the Desert Southwest will continue to build into the PacNW and into western Canada. During this period, confidence is mod-high (60-85%) that by the end of the workweek a warming trend will bring temperatures back into the lower to mid 90s in the lower elevations, with temperatures warming into the mid to upper 90s over the weekend. A drying trend during this period will also result in widespread RHs into the mid teens to lower 20s by Friday, while winds will remain light through most of the period. Lawhorn/82 && .PRELIMINARY POINT TEMPS/POPS... PDT 86 57 87 58 / 10 0 0 0 ALW 88 62 88 63 / 20 0 0 0 PSC 90 59 91 59 / 20 0 0 0 YKM 87 56 89 59 / 10 0 0 0 HRI 88 59 90 61 / 10 0 0 0 ELN 82 56 84 57 / 10 0 0 0 RDM 84 46 86 47 / 0 0 0 0 LGD 88 54 91 54 / 10 0 0 0 GCD 90 51 93 52 / 0 0 0 0 DLS 83 59 86 62 / 10 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...82 LONG TERM....82 AVIATION...75