Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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532 FXUS66 KPDT 232128 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 228 PM PDT Mon Sep 23 2024 .SHORT TERM...Today through Wednesday... Bottom Line Up Front 1. Dry and warm conditions through mid week 2. Breezy conditions Wednesday 3. Chances of widespread precipitation Wednesday Models are in firm agreement with the upper level ridge moving in over the region today. With the ridge will come increased temperatures across the region with at or slightly above near normal temperatures with the highest temperatures occurring Tuesday. With the amplitude of the ridge tilted and slightly flattened, models show the majority of the warm temperatures will be centered around the axis of the ridge which happens to be over central OR. Roughly 72% of the raw ensembles show central OR to be in the low 90s Tuesday. Models have also highlighted central OR with moderate HeatRisk due to the high daytime temperatures coupled with the overnight highs remaining elevated overnight. Models show that on Wednesday an upper level trough will slip down the Canadian coast and move towards the PacNW. Surface pressure models show a tightening of the pressure gradient along the Cascades with a shortwave embedded within it. This will bring enhanced winds through the Cascade Gaps as well as spill out across the entire CWA. Looking at the probabilities of 25 mph or greater winds across the area, dang near the entire region, minus Wallowa, will see 80-100% probabilities of sustained winds of 25 mph or greater. Looking at the probabilities of 39 mph or greater, the zones that show the best promise, over 80% probabilities, are the Simcoe Highlands, foothills of the Southern Blues, Yakima and Kittitas Valleys. Very isolated pockets will see winds above that and there are currently no advisories in effect as it remains below criteria. Not only do the models show the upper level trough moving over, it also shows a tail of moisture following along with it. However, models do show some timing and amount differences. Blended a few of the models together to achieve the forecasted amounts for Wednesday; Raw ensembles show 80-100% probabilities of 0.1-0.3 inches of rain along the crests, 30-50% probabilities of 0.05-0.1 inches for the east slopes of the Cascades, 30-40% for 0.03 inches for the Blue Mountains and 30-40% of the raw ensembles show the Gorge, foothills of the Blues and the Columbia Basin will see up to 0.01-0.3 inches of rain. Bennese/90 .LONG TERM...Thursday through Monday...Ensemble NWP models are in very good to excellent agreement that a weak frontal system will impact the Washington Cascades late Thursday through Friday morning. Confidence in measurable light rain is medium-high (50-70%), with lower (30-50%) chances of a wetting rain (0.10" or greater). Elsewhere, chances of rain are very low (<15%). Friday through Saturday morning, confidence is high (>70% chance) that dry conditions will prevail with quasi-zonal flow aloft. Saturday afternoon through Sunday, ensemble clusters suggest increasing uncertainty in the 500-mb pattern over the PacNW; roughly 40% advertise a shortwave trough of varying amplitude, while the remainder suggest an upper-level ridge extending northward into Canada. Monday, the favored solution is an upper-level ridge over the PacNW and Intermountain West (44% of members), while 23% of members keep the ridge axis centered just offshore. The remaining cluster solutions show either a deep upper low digging across the Intermountain West (8%) or a 500-mb zonal jet extending into the PacNW with our CWA on the southern (warm) side. Whichever solution verifies, ensemble agreement in any climatologically unusual weather events is low per the ECMWF EFI. Plunkett/86 && .AVIATION...18Z TAFs...VFR conditions are forecast for all sites through the TAF period, with low chances (<30%) of smoke/haze reducing CIGs/VSBYs to sub-VFR again overnight into Tuesday morning at BDN/RDM. Otherwise, predominantly FEW-BKN high-level clouds through the day, becoming SKC to FEW250 overnight through Tuesday at TAF sites. Sustained winds of 10 kts or less, diurnally driven for all sites. Plunkett/86 && .PRELIMINARY POINT TEMPS/POPS... PDT 54 88 58 83 / 0 0 0 10 ALW 56 90 63 87 / 0 0 0 20 PSC 57 88 61 87 / 0 0 0 10 YKM 54 87 55 81 / 0 0 0 30 HRI 56 90 59 85 / 0 0 0 10 ELN 55 88 56 78 / 0 0 0 30 RDM 49 91 53 81 / 0 0 0 10 LGD 49 86 57 87 / 0 0 0 10 GCD 50 86 54 85 / 0 0 0 10 DLS 59 93 61 78 / 0 0 0 30 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...90 LONG TERM....86 AVIATION...86