Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
014 FXUS66 KPDT 132033 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 133 PM PDT Sat Sep 13 2025 .DISCUSSION...Satellite imagery reveals an upper-level ridge of high pressure over the Pacific Northwest. Meanwhile, broad troughing, with multiple embedded waves, is present downstream. Upstream, another broad trough is located just offshore, and a well-defined cold front is also visible over the ocean. This trough, and attendant surface cold front, will drive our weather tonight through Sunday before exiting the region to the east through Monday. This afternoon, a cumulus field has developed over the Blue Mountains and central Oregon Cascades. Cannot rule out an isolated shower through this evening, but probabilities are low at 10% or less, highest for the northern Blue Mountains region. Overnight, scattered to numerous showers are forecast, with the most noteworthy area to the lee of the Cascades from central Oregon through the lower Columbia Basin and farther east into the Blue Mountains and their foothills. Forecast soundings from CAMs suggest some modest (250-500 J/kg) MUCAPE and ample moisture (PWATs generally 0.7-1.3"). This, coupled with good synoptic-scale forcing as the vort max slides onshore, should induce the aforementioned showers and also facilitate a slight chance of embedded thunderstorms. Of note, the ECMWF EFI for QPF does highlight a region of 0.6-0.8 roughly from the Tri-Cities southeastward through the northern Blue Mountains for 00Z Sunday to 00Z Monday. Breezy westerly winds (generally 10-20 mph with gusts of 20-35 mph) will accompany frontal passage Sunday morning and continue through afternoon in the front`s wake. Confidence in advisory- level sustained winds or gusts is low (20-40%) except for the most wind-prone areas of the eastern Columbia River Gorge and Kittitas Valley where there are locally higher chances (50-80%) of peak wind gusts reaching advisory levels (45 mph or higher). Drier conditions will return Monday through much of Wednesday as another ridge of high pressure moves over the Pacific Northwest. Late Wednesday into Thursday, ensemble means and clusters suggest another upper-level trough will approach from the Pacific. Uncertainty burgeons by Friday, with roughly half of ensemble members showing some form of a closed low over the Pacific Northwest while the other half show weaker troughing overhead with a more pronounced low off the southern California coast. The former solutions would generally be cooler and wetter, while the latter would be warmer and drier. Confidence is medium-high (60-80%) in breezy to windy westerly winds through the Cascade gaps and wind-prone portions of the Columbia Basin and Blue Mountain foothills on Wednesday. NBM probabilities of advisory-level gusts are still low (20-50%), highest for the eastern Columbia River Gorge and Kittitas Valley. That said, raw guidance has piqued my interest; 12Z deterministic NWP runs are showing 8-12 mb surface pressure differences from PDX to GEG, and the raw output from the ECMWF ensemble is also suggesting Wednesday has potential for advisory-level winds. Plunkett/86 && .AVIATION...18Z TAFs...Mostly clear skies this morning will become SCT-BKN (mid- and high-level cloud) by this evening as a weather system approaches from the Pacific. BKN-OVC skies are then forecast overnight through Sunday morning, and all sites have a 30-50% chance of rain showers along and ahead of a cold frontal passage. Thunder chances are low (15% or less), but cannot rule out isolated embedded thunderstorms within the broader region of showers. The overnight timing of the cold frontal passage reduces confidence in TAF details to medium (40-60%) due to uncertainty in winds, and of course exact timing/location of showers. Additionally, sub-VFR conditions may occur in showers and/or thunderstorms, but confidence was too low (<30%) to include any mention in the 18Z TAFs. Plunkett/86 && .PRELIMINARY POINT TEMPS/POPS... PDT 56 71 48 73 / 20 80 30 0 ALW 61 71 52 73 / 10 80 40 0 PSC 59 75 50 75 / 30 70 20 0 YKM 57 75 46 76 / 20 60 10 0 HRI 59 74 50 75 / 30 70 20 0 ELN 53 71 45 75 / 10 60 20 0 RDM 51 68 35 74 / 50 50 0 0 LGD 53 66 42 72 / 10 90 40 10 GCD 53 68 41 74 / 20 80 20 0 DLS 61 74 49 79 / 30 60 10 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...86 LONG TERM....86 AVIATION...86