Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
678 FXUS66 KPDT 140711 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1211 AM PDT Sun Sep 14 2025 Updated Aviation Discussion .AVIATION...06z TAF UPDATE...Amended BDN and RDM to include mention of -tsra overnight, as some isolated thunderstorms have formed over Lake County late this evening and look to move toward both sites. Evans/74 && .PREV DISCUSSION... /issued 1038 PM PDT Sat Sep 13 2025/ AVIATION...06z TAFs...A cold front is expected to bring shower chances to all TAF sites starting overnight, becoming more widespread by around daybreak Sunday. Localized MVFR conditions may occur as a result. Showers will move out of most of the forecast area by late Sunday morning, however isolated showers may develop near PDT,ALW, and PSC during the afternoon and evening hours (20-30% chance) Sunday. A few showers may contain isolated thunderstorms, however confidence was not high enough to include mention of ts anywhere in the TAFs. Winds will also pick up behind this front across all sites heading into Sunday afternoon, with W/NW gusts up to 25 kts expected. PREV DISCUSSION... /issued 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 && .PRELIMINARY POINT TEMPS/POPS... PDT 47 73 48 81 / 50 0 0 0 ALW 52 74 53 83 / 50 0 0 0 PSC 49 75 48 83 / 40 0 0 0 YKM 45 76 49 82 / 10 0 0 0 HRI 48 75 48 82 / 30 0 0 0 ELN 44 75 46 80 / 10 0 0 0 RDM 35 74 38 83 / 0 0 0 0 LGD 42 72 43 80 / 60 0 0 0 GCD 40 74 43 82 / 30 0 0 0 DLS 48 79 52 86 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...86 LONG TERM....86 AVIATION...74