textproduct: Pendleton

KEY MESSAGES

- Dry conditions through Sunday morning

- A return of active weather late Sunday afternoon into Monday with light precipitation in the mountains

- More widespread precipitation chances, breezy winds, and cooler conditions Wednesday through Thursday

DISCUSSION

Afternoons become breezy Today and a little more windy in a few spots on Sunday. This is focused across the higher terrain and mountain zones above 2500-3000 feet, such as the Simcoe and JohnDay/Ochoco Highlands and Kittitas/Yakima Valleys and in the 3 to 7 pm window. Sunday night, a weak atmospheric river will influence the Interior Northwest with a broad 200-300 kg/ms IVT, and a max of about 18 to 22 mm IVW into the Lower Columbia Basin. This appears mainly a mountain and highlands episode as snow levels crash behind the cold front as the precipitation probability ramps downward on Monday. During the time frame of expected peak PoPs, the snow levels are expected to range from around 3000-3500 ft AGL across the WA Cascades and around 4500-6000 ft AGL over the northern Blue Mountains. Limited winter weather impacts in part sue to warm road temps (currently in the 40-60 degree surface temps even hours before peak heating Today).

Monday and Tuesday appear similar in terms of winds and wind gusts across the forecast area with winds in the 10 to 15 mph range for gusts in the lowlands and higher gusts ranging from 15 to 30 mph into higher terrain. A stronger AR is forecast by the ensembles and EC/GFS control runs to develop Wednesday (extending through Thursday) with more meaningful impacts in terms snow for the mountain zones and and windy conditions over a wider area. The WWRF (GFS/EC) 9km freezing level plan view shows the cold front moving across the region by Wednesday. NBM ensemble mean at this time would have the crests of the Washington and Oregon Cascades receive around 1 foot on average of snowfall with a couple of feet up on the cone tops. As far as pass level impacts, the WSSI-P gives a 50 to 70% chances for minor impacts based on snowfall alone, as the highest snow amounts from the of the NBM mean along I-90 is 5 to 7 inches locally. What does fall will be a heavy wet, low SLR snow with higher probabilities impact from snow load than snow amounts.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Limited aviation concerns the next 24-hrs with VFR prevailing area-wide. Latest satellite shows limited sky cover with some areas of mid clouds and high clouds passing across eastern OR. A modest cross-Cascade pressure difference in place with gusts 22 kts and higher across the eastern Gorge spilling into the Lower Basin, along the Kittitas Breezeway, and central OR. Peak gusts as high as 30-35 kts seen with these winds with winds lessening this evening. Meanwhile, winds overnight will be light and generally 4-8 kts with light/variable in the central OR terminals. Winds will then increase again tomorrow ahead of an approaching disturbance with the best precip chances confined to the crest of the Cascades and central Gorge. Low confidence in any TAF terminals seeing precip with the best chances (10-30%) at KDLS and KALW.

Preliminary Point Temps/PoPs

PDT 37 54 31 50 / 0 20 30 10 ALW 41 54 34 50 / 0 40 50 10 PSC 39 59 34 56 / 0 20 10 0 YKM 35 57 28 53 / 0 10 0 0 HRI 39 57 32 54 / 0 20 10 0 ELN 33 50 26 48 / 0 10 10 0 RDM 32 57 24 51 / 0 10 0 10 LGD 35 57 31 47 / 0 30 70 20 GCD 36 63 31 48 / 0 10 40 30 DLS 40 56 33 57 / 0 30 10 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.