Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
815 FXUS66 KPDT 092155 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 255 PM PDT Sun Mar 9 2025 .SHORT TERM...This afternoon through Tuesday night...Mild temperatures (predominantly upper 50s to upper 60s for population centers) are present across the forecast area this afternoon as the region is on the south (warm) side of the polar jetstream. An elongated trough stretching from British Columbia southwest to off the southern California coast is splitting apart with the dominant circulation developing in the vicinity of 31N, 132W. This feature will not impact the PacNW, though the weaker shortwave and its attendant cold frontal boundary will slowly move southeast late this afternoon, tracking inland overnight. The main weather concerns associated with this system will be breezy to locally windy southerly to westerly winds nearly area- wide this afternoon (with ample mixing of higher-momentum air from aloft) and tonight (with frontal passage). While some ridgetop locations have seen gusts in excess of 45 mph, confidence is only medium (40-60%) in localized gusts of 40-45 mph in the Columbia Basin and along the Blue Mountain foothills this afternoon and tonight, so no wind highlights have been issued. With regard to snowfall, confidence is medium-high (50-80%) in light snowfall for the mountain passes of the OR/WA Cascades and northern Blue Mountains. In general, 1-3" are forecast for the Oregon Cascades, 2-6" for the Washington Cascades, and 1-3" for the northern Blue Mountains. Confidence is low (<30%, except localized spots) in advisory-level snowfall amounts being reached, especially given that the cold frontal band is expected (>80% confidence) to fall apart through Monday morning as it tracks over the Blues. A second, more organized system, is forecast to approach the Pacific Northwest late Tuesday with precipitation spreading across the forecast area by Tuesday night as the upper trough and attendant cold front come onshore. Plunkett/86 && .LONG TERM...Wednesday through Sunday... Bottom Line Up Front 1. System 1, Wednesday through Thursday, will bring snow above 2000 feet with low elevation rain with breezy winds and cooler temperatures. 2. Brief break in systems Thursday night into Friday morning 3. System 2, Friday morning through Sunday, will bring snow above 2000 feet with low elevation rain with breezy winds and cooler temperatures again. The long term will be characterized by multiple weather systems gracing the region. Models are in relatively good agreement through the long term with regards to the systems however, clusters do show a bit of variance with the timing and the overall strength of each system as they approach. Models show system 1 to arrive Wednesday morning and tracking across the region a bit slowly lasting through Thursday night. Looking again at the clusters for this timeframe, the main variances as of now are with timing and positioning of the system. Deterministic guidance shows the timing to be slight. Regardless, the cold front associated with the upper level system will bring the snow levels to near 2000 feet and precipitation will fall as snow. The front will also cause temperatures to drop 2-5 degrees below seasonal normal with EFI in agreement that the highs will settle in the 50s for the Gorge, Basin and foothills, low 50s for central OR and 30s for the higher peaks with overnight lows dropping below freezing across the vast majority of the region. Raw ensembles are showing Snoqualmie Pass to have over a 30-40% probability of 5-7 inches, Santiam Pass has 20-40% probabilities for 5-7 inches and White Pass 30-50% probabilities of 3-4 inches. Moving to the Northern Blues, raw ensembles show 40-50% probabilities of Tollgate and Ski Bluewood seeing 5-6 inches. As for the remainder of the region below 2000 feet will see rain. 20-30% of the raw ensembles showing the Basin, central OR and north central OR seeing 0.10-02.0 inches of rain while the remainder of the area such as the foothills of the northern Blues will see 40-60% probabilities of 0.20-0.30 inches of rain. Lastly, the front will also bring with it breezy conditions across the majority of the lower elevations with 40% probabilities of gusts to 25 in central and north central OR, 30-50% through the Basin, Gorge and along the foothills of the Blue Mountains. Winds will settle overnight before picking up again Friday however, gusts will be a bit weaker than Thursday. Thursday night overnight into Friday morning models show system 1 to exit the area and the upper level flow flatten and turn to a more westerly component. EFI shows temperatures to be 5 to 10 degrees colder than what is seasonally normal. Highs will be in the low 50s for the Gorge, Basin and adjacent valleys, north central OR and the foothills of the Blues while the remainder of the area will be in the 30s to low 40s. There will be some lingering precipitation Friday along the higher peaks of the Cascades ahead of the next system, over 80% of the raw ensembles show probabilities of the higher peaks seeing an additional 1-3 inches, especially along the OR Cascades. Winds will be elevated Friday with over 60% probabilities of gusts between 20-25 mph. Models are in decent agreement with system 2 arriving arriving Friday morning/early afternoon and persisting through Sunday evening. Clusters again showing the main variance being with the timing and positioning of the system. Looking at the vapor transport ensembles, there is between a 40-60% chance the system will slam right into the PacNW bringing plenty of precipitation back to the region. Another cold front is associated with this next upper level trough yet again bringing snow levels to at or near 2000 feet. Looking at raw ensembles as well as deterministic data, this system will pack a punch that is for sure. Now how much of a punch is what is still in question as confidence in the forecast is high regarding the system itself however, as of right now one can say we are moderately to highly confident (70+%) in the forecast that this will be a decent system with plenty of precipitation. With that said, confidence in snow amounts teetering on advisory levels this far out is moderate (50-60%) at best. EFI is showing at or below average temperatures with areas continuing to see 2-5 degrees below seasonal normal with isolated areas seeing nearly 5-10 degrees. EFI is also suggesting abnormally high winds for this time of year with raw ensembles showing agreement. With this being days 7 and 8, confidence again is moderate at best concerning the strength of the wind gusts. This system and the associated wind potential will continue to be monitored. Bennese/90 && .AVIATION...18Z...VFR conditions expected through the forecast period at all TAF sites with a PROB30 for MVFR due to rain showers bringing VIS to 4SM briefly around 06Z at DLS. Issue for the period will be with the winds ahead of the incoming system. Winds are already heightened across BDN/RDM with 12kts and gusts to 20kts. YKM/DLS will see an increase near 21Z before spreading to PSC/ALW/PDT after 03Z with 12-14kts and gusts to 23kts. Bennese/90 && .PRELIMINARY POINT TEMPS/POPS... PDT 39 54 37 56 / 20 20 10 20 ALW 40 52 38 53 / 30 30 20 30 PSC 39 57 35 56 / 10 0 0 10 YKM 32 53 33 51 / 20 0 0 10 HRI 39 57 36 56 / 20 10 10 20 ELN 31 50 31 49 / 20 0 0 10 RDM 32 54 31 56 / 10 10 0 10 LGD 36 50 35 53 / 20 30 20 20 GCD 35 53 34 54 / 0 10 10 20 DLS 38 55 37 55 / 60 10 10 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...86 LONG TERM....90 AVIATION...90