781 FXUS66 KPDT 080005 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 505 PM PDT Mon Apr 7 2025 .UPDATED AVIATION DISCUSSION... .AVIATION...TAFs 00Z...All sites are VFR for this evening of this TAF period. Pockets of showers and thunderstorms affected KDLS, KPDT, KALW, and KPSC through 00Z. For tonight, the weather should be calm for all sites with mid to high clouds. KDLS/KALW/KPSC will have the potential to see outflow winds up to 30 kts from dissipating showers/storms through 02Z. Showers may return tomorrow morning for KDLS and KYKM along with gusty winds (25-35 mph) at KPDT, KRDM, KBDN, KYKM, and KPSC when a frontal system makes landfall. Feaster/97 && .PREV DISCUSSION... /issued 209 PM PDT Mon Apr 7 2025/ .SHORT TERM...Today through Wednesday... 1. Isolated thunderstorms along the Cascade ridges and eastern mountains this afternoon and Tuesday afternoon. 2. Isolated showers will continue through Tuesday 3. Drying and warming begins again Wednesday Current radar imagery is showing some showers moving across the region from north central OR across the foothills of the Blues as well as along the eastern slopes of the WA Cascades through Yakima and Kittitas Valleys. So far little to no indications of lightning from any of the cells with the exception of 1 strike in Kittitas Valley. The brief clearing of the sky between these systems is enough daytime heating to assist with isolated thunderstorms popping up between now and within the next few hours. Looking at the CAMs models coupled with the ensembles, confidence in isolated thunderstorms has increased to 30-40%. Models show MUCAPE values to be between 200-300 J/kg, LIs between -1 and -3, lapse rates of 8.3 C/km and higher with moderate bulk shear of 35 knots. All of these ingredients coupled with the orographic lift and daytime heating has allowed confidence to increase to the lower end of moderate probabilities of 30-40%. With the incoming showers bringing more cloudy skies across the region overnight and into Tuesday, CAMs models and ensembles are showing a decrease in all the ingredients needed for thunderstorm initiation. With the said, only 5-10% of the raw ensemble members show thunderstorms across the area tomorrow. As mentioned above, precipitation will continue today through tomorrow as the upper level system continues pushing onshore. Much of the moderate/heavy precipitation will stay along the crests of the Cascades with 70-90% probabilities of 0.50 inches of rain with light snow above 5000 feet today decreasing slightly overnight then ramping back up again tomorrow with 80-100% probabilities of near 0.50 inches of additional rain. The Blue mountains of northern OR will also see 60-80% chances of 0.25 inches of rain Monday and another round Tuesday. The remainder of the region except central, north central Yakima and Kittitas Valleys will see 30-50% chances of between 0.10-0.20 inches of rain decreasing to 10-30% chances of 0.01-0.05 inches Tuesday. Lastly, models show an upper level ridge beginning to back build into the region Wednesday. With the incoming ridge, ensembles as well as deterministic guidance shows the region to be under the influence of drier and a bit warmer conditions. Bennese/90 .LONG TERM...Thursday through Monday...An upper level ridge will be over the Pacific Northwest on Thursday and will bring unseasonably warm temperatures to the area. This ridge will move eastward into Friday as the next weak trough approaches the coast. Precipitation will develop later Thursday into Friday, mainly over the mountains. A second, deeper trough will bring another shot of precipitation, also mainly for the mountains Friday night into Saturday. A ridge will then build back in bringing more dry weather and warming temperatures for Sunday into Monday. QPF amounts are fairly light, generally 0.25 inches or less over the Cascades Thursday into Friday and even less Friday into Saturday only perhaps up to 0.10 inches. Model guidance is in very good agreement through Monday, then there are some discrepancies, but these involve a ridge and little sensible weather. Snow levels will remain quite high, generally over 5000 feet. However, as the second trough moves onshore, they will drop to between 2000 and 2500 feet in the Washington Cascades and 3000 4000 feet most elsewhere. However, due to the high snow levels, little if any snow accumulations are expected. There will be some diurnally breezy winds Friday, but especially Saturday with the trough especially across the Simcoe Highlands, Kittitas Valley, Columbia Basin and Blue Mountain Foothills. Winds could gust in the 25 to 35 mph range. The NBM probabilities of wind gusts >= 25 mph are 70 90 percent across much of the area. However, the probabilities of wind gusts >= 39 mph are 50 to 70 percent across the previously mentioned locations and about 80 percent in the Kittitas Valley. Due to the warm temperatures and snow melt, rivers will continue to run high, especially the John Day and Naches and portions of the Grande Ronde. High temperatures will range about 10 degrees above normal on Thursday. The ECMWF EFI does key in on these temperatures, with 0.6 to 0.7 anomalies for much of eastern and central Oregon, with an area of 0.7 to 0.8 anomalies for portions of the Blue Mountain Foothills and points east. Highs be closer to normal Friday and then will be a few degrees below normal on Saturday and Sunday before rebounding on Monday. && .PRELIMINARY POINT TEMPS/POPS... PDT 40 62 41 65 / 50 60 30 0 ALW 42 60 41 62 / 70 70 50 10 PSC 42 65 39 67 / 10 40 10 0 YKM 37 60 34 63 / 10 50 0 0 HRI 39 65 39 67 / 20 50 20 0 ELN 36 57 34 60 / 30 60 10 0 RDM 32 60 33 67 / 10 30 10 0 LGD 37 58 37 61 / 80 60 60 10 GCD 35 57 36 64 / 50 40 20 0 DLS 41 61 41 66 / 40 80 20 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...90 LONG TERM....77 AVIATION...97