Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
328 FXUS66 KPDT 140607 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1107 PM PDT Wed Aug 13 2025 .AVIATION...06Z TAFs...VFR conditions are forecast for all sites through the valid period. That said, a plume of smoke present in central Washington north of YKM is anticipated to shift southward overnight into Thursday morning. Sub-VFR VSBYs may occur at YKM, and PSC if the plume reaches that far southeast, but confidence in timing and magnitude of VSBY reductions was too low to mention in the 06Z TAFs. Periods of breezy winds will continue through Thursday, strongest during the afternoon and evening hours. Other than some mid/high cloud passing overhead in advance of a weather system approaching from the Pacific, some low stratus (2-5 kft AGL) may form over BDN/RDM/ALW/PDT overnight into early Thursday morning (confidence 30-50%). Confidence in sub-VFR CIGs at the aforementioned sites is low (<30%). Rain chances are very low (<10%) except at YKM where a PROB30 group was included from 04-06Z Friday. Plunkett/86 && .PREV DISCUSSION... /issued 849 PM PDT Wed Aug 13 2025/ EVENING UPDATE...Winds have dropped below advisory thresholds in the Kittitas Valley, so the Wind Advisory was allowed to expire at 8 PM PDT. Relative humidity has risen across the region such that Red Flag conditions are no longer being met, so the Red Flag Warnings were cancelled early. Plunkett/86 && .PREV DISCUSSION... /issued 146 PM PDT Wed Aug 13 2025/ DISCUSSION...Satellite imagery this afternoon shows mostly clear skies across the eastern PacNW, though road/fire cameras at the surface show plenty of haze from blowing dust and smoke. Today through Thursday: A dry upper shortwave and surface cold front will move across the region, continuing to produce breezy to windy conditions across the lower elevations. Strongest gusts up to 50 mph are expected to develop through the Kittitas Valley and along exposed ridges of the WA Cascade east slopes through late this afternoon (confidence 80-90%). Relative humidities will also dip below critical thresholds (10-20%) this afternoon, and combined with the elevated winds, has resulted in widespread critical fire weather conditions from central OR to the Columbia Basin and adjacent valleys. While this system will remain dry, there is a slight chance (15-25%) for light showers to develop along the Cascade crest late this evening and into the overnight hours. By tomorrow, broad troughing with weak flow aloft will develop over the PacNW, with the forecast area remaining dry, though temperatures will be on a cooling trend as a cooler airmass advects into the region. Winds will remain breezy to locally breezy in the lower elevations as pressure gradients will be slow to weaken tonight and tomorrow. Friday through Sunday: Confidence continues to increase (75-90%) that a cooler, wetter pattern will develop across the PacNW beginning with a cold front passage Friday into Saturday, with several shortwaves/shortwave impulses swinging around the bottom of a broad upper low in the Gulf of Alaska through Sunday. A weak atmospheric river (AR) will accompany the passage of the cold front, increasing PWATs to 0.7 to 1.1 inches across forecast area, allowing for plenty of moisture to work with through the weekend. As for convection, instability will be lacking across the region for Friday, with low confidence (10-15%) that the cold front will be enough to produce a thunderstorm or two across the mountainous terrain. As for Saturday and Sunday, flow aloft will back to the southwest, with surface based instability increasing in the afternoon across central OR, OR Cascade east slopes, and the eastern mountains. This will result in chances (15-30%) of isolated to widely scattered thunderstorms to develop in the afternoons and early evenings. With seasonably high PWATs across the region, these thunderstorms will be capable of moderate to heavy rainfall and small hail, with abundant lightning. While lightning may be abundant, the increased rainfall with these storms will keep the potential for new fire starts low. Moderate- High confidence (70-85%) that temperatures will cool into the upper 70s to mid 80s through the weekend. Monday through Wednesday: Good agreement amongst ensemble cluster members (ECMWF, GFS, Canadian) that upper level troughing will dig equatorward off the west coast, increasing the southerly component of flow aloft into the PacNW. By Monday, ensemble members begin a drying trend across the forecast area, but keep modest instability across the eastern mountains through Tuesday evening(confidence 55-75%). This will result in isolated thunderstorm chances (10-20%) across the mountains each afternoon. With conditions gradually drying out, these thunderstorms will likely be drier, increasing the fire weather concerns going into the middle of next week. By Wednesday, ensemble members are in good agreement of the upper trough broadening over the eastern Pacific, and in turn turning flow aloft more westerly and reducing the chances of isolated thunderstorms over the eastern mountains (confidence 45-65%). Moderate confidence (50-70%) that temperatures will warm back into the mid 80s with locally lower 90s early next week. Lawhorn/82 && .PRELIMINARY POINT TEMPS/POPS... PDT 60 84 60 85 / 0 0 0 10 ALW 64 84 64 85 / 0 0 0 10 PSC 60 87 63 86 / 0 0 0 10 YKM 59 86 62 81 / 0 0 20 40 HRI 62 85 63 86 / 0 0 0 10 ELN 58 80 59 77 / 0 0 30 50 RDM 50 82 52 82 / 0 0 0 10 LGD 55 84 54 85 / 0 0 0 0 GCD 54 86 52 87 / 0 0 0 0 DLS 63 81 67 80 / 0 0 20 40 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ EVENING UPDATE...86 SHORT TERM...82 LONG TERM....82 AVIATION...86