textproduct: Pendleton

KEY MESSAGES

- A return of active weather late This Afternoon into Monday with light precipitation in the mountains

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

DISCUSSION

A narrow band of mid level moisture was tracking inland noted by the GOES Airmass RGB satellite imagery and NAM model 700 to 300 mph mean winds of around 60 knots across the Columbia basin. EC and GFS AR models would have this weak band of 200-300 IVT moisture east of the forecast area by 12 Monday. High confidence (80-90%) for additional snows across the Upper Eastern slopes of the WA Cascade crest begins this evening however these chances wane to near zero by the overnight as the jet/speed max passes. WSSI-P hints at around a 10-40% chance for minor impacts owing to snow (winter driving conditions). The better chances (40%) are toward higher terrain above the snow ski area at Snoqualmie, through about 5 pm Monday. Rain (lower elevations) and snow (Mountain zones) showers will be a possibility Monday night though late Tuesday across the eastern slopes of the Oregon Cascades as well as the over the John Day/Ochoco Highlands and southern Blue Mountains (10% north to 50% south). Tuesday will also be characterized by light surface winds areawide and mostly cloudy elsewhere, with only a slight bump in afternoon high to the mid 50s in the Highland valleys and Lower Columbia basin.

As far as the clusters relevance to the medium range, the setup looks like a high confidence, generally lower impact progression with no noticeable Shift of Tails. A cold front moves through Wednesday dropping the snow levels and bringing dominant snow p-type to all of the pass levels in the Cascades, and the Northern Blue Mountains. WSSI-P show no reasonable chances for moderate impacts across the WA Cascades Wednesday through Thursday, but about a 40 to 50 percent chances for like impacts across the eastern slopes of the Oregon Cascades, especially Deschutes county. The 24 hr snowfall spread ending 5 am Thursday is 3 to 6 inches (25 to 75 percentiles ). Greater impacts might be found at the Santiam pass where the like range is from 3 to 8 inches where a section of highway 20 can get 6 on the lower end and 12 on the higher end around Mt. Washington. The areas along the Oregon Cascades should have a bit of a longer duration snow episode as well that winds down into Thursday night. Given aforementioned uncertainties from the WSSI, am planning to hold off on winter weather headlines (any watches) at this time. Russell/71

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

VFR conditions currently at all sites, which will stay the course through the period. An incoming system has dropped ceilings to between 6-10kft, with KRDM/KBDN expected to drop further to around 3.5kft this evening. Breezy winds have also initiated across most sites as gusts of 20-30kts are anticipated to persist into the early evening. Winds will subside tonight as ceilings lift and break related to high pressure moving in behind the departing system. 75

HYDROLOGY

Some rivers begin showing a response by Wednesday evening as they are already sensitive to additional rains on elevated river levels. However all of the forecast hydrographs at this time are indicating cresting below the actions stages late in the week. Russell/71

Preliminary Point Temps/PoPs

PDT 32 50 27 53 / 20 0 0 10 ALW 34 50 31 54 / 30 10 0 10 PSC 34 55 28 58 / 10 0 0 0 YKM 29 53 28 55 / 10 0 0 0 HRI 32 54 27 56 / 10 0 0 0 ELN 26 48 26 50 / 10 0 0 0 RDM 27 50 25 54 / 10 20 10 10 LGD 32 48 25 55 / 50 20 0 10 GCD 32 49 30 56 / 20 40 20 40 DLS 33 57 32 57 / 20 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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