Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
997 FXUS66 KPDT 011740 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 940 AM PST Mon Dec 1 2025 Updated Aviation Discussion .AVIATION...18z TAFs...Low clouds and patchy fog continue for PSC this morning, otherwise VFR conditions prevail across the forecast area. Expect bkn-ovc cigs 7-10 kft throughout the day, with some clearing early in the evening before the next frontal system arrives by early morning Tuesday. IFR conditions may linger in PSC over the next couple of hours, before seeing relief by the afternoon. Not expecting precip with this next system across most TAF sites, however PDT and ALW may see light rain showers beginning at or just before sunrise, ending by the end of the TAF period. Winds will generally be light and variable today, becoming more W/NW overnight ahead of this next front. 74 && .PREV DISCUSSION... /issued 350 AM PST Mon Dec 1 2025/ DISCUSSION...An upper-level ridge of high pressure is in place over the Pacific Northwest early this morning. Aside from chilly temperatures ranging from the upper single digits to upper 20s and some areas of low stratus and patchy fog, the remainder of the night and morning is expected to be uneventful. Later this morning through afternoon, the first in a series of shortwaves embedded within northwesterly flow aloft will track over the forecast area. While this first shortwave, currently visible in water vapor imagery extending southwest from the northwest end of Vancouver Island into the Pacific, will be weak, there is a 10-30 percent chance of light precipitation with the wave. The main event, a stronger shortwave, is advertised by ensemble NWP guidance to arrive this evening, subsequently crossing overhead tonight through Tuesday night before exiting to the south and east through Wednesday morning. While upper-level dynamics don`t look quite as good with this shortwave compared to the compact closed low that brought low-elevation snowfall to the region Friday evening, deep northwesterly flow should facilitate orographic precipitation, especially over the northern Blue Mountains and other favored areas of northeast Oregon. Was previously expecting a better moisture tap with this system; however, that no longer appears to be the case as forecast soundings from the HREF and REFS show PWATs of 0.3-0.6 of an inch again. Snow chances are low across the Blue Mountain foothills and eastern half of the Columbia Basin (10-30 percent chance of measurable snow per NBM guidance), but better chances (50-70 percent) of at least 4 inches of snow are shown for the northern Blue Mountains. Advisory-level snowfall is possible (20-45 percent chance) across the northern Blue Mountains, but confidence was too low to issue any winter headlines at this time. Part of what is driving uncertainty in the amount of snowfall is the vertical depth of moisture, specifically whether or not saturation will extend into or through the dendritic growth zone (DGZ). While a couple members of the HREF and REFS do exhibit saturation through the DGZ, most only extend partially into the zone (or not at all) which would limit snowfall efficiency. Ensemble guidance is still suggesting some locally breezy westerly winds through the Cascades gaps on Tuesday. Mostly dry conditions are expected (70-90 percent chance) Wednesday into Thursday morning as upper-level ridging returns to the Pacific Northwest. By the end of the week, ensemble solutions begin to diverge with regard to pattern details, but a transition to a more zonal upper-level pattern is present among all ensemble clusters beginning Friday and extending through Sunday. As far as tangible weather, this would result in warmer, wetter, breezier conditions. Of note, EFI values ranging from 0.5-0.8 across the Columbia Plateau are pointing to decent ensemble agreement in windy conditions relative to model climatology from 00Z Saturday to 00Z Sunday. Moreover, NBM probabilistic guidance suggests low-medium (20-60 percent) chances of advisory-level wind gusts Friday through Sunday, and there is low potential (10-20 percent chance) for a high-end wind event late Friday and Saturday across the region. && .PRELIMINARY POINT TEMPS/POPS... PDT 37 29 40 27 / 10 40 70 10 ALW 36 31 38 29 / 20 50 80 20 PSC 36 27 40 25 / 10 30 30 0 YKM 38 25 44 23 / 10 20 10 0 HRI 37 28 41 27 / 10 30 50 0 ELN 37 26 43 22 / 20 30 10 0 RDM 48 27 46 21 / 10 10 10 0 LGD 42 32 41 26 / 10 50 90 20 GCD 46 31 43 27 / 10 30 60 10 DLS 42 35 50 34 / 20 20 20 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ DISCUSSION...86 AVIATION...74