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 /06Z TAFS THROUGH 06Z TUESDAY/

VFR conditions prevail through the period. Breezy conditions continue in the DLS/PDT and, to a lesser extent, at PSC. Winds are expected to decrease to around 10-15 knots heading into the later morning. Otherwise, mostly dry conditions through the 24-hour period, except for some slight PROB30 of rain showers in the Central OR sites.

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 57 32 50 28 / 20 20 10 10 ALW 56 34 50 31 / 40 30 10 0 PSC 60 34 56 29 / 20 10 0 0 YKM 58 29 53 28 / 10 10 0 0 HRI 59 32 54 28 / 10 10 0 0 ELN 51 26 48 26 / 10 10 0 0 RDM 61 27 49 29 / 0 10 30 20 LGD 60 32 48 26 / 20 50 40 10 GCD 64 32 48 32 / 10 20 70 40 DLS 57 33 57 32 / 30 10 0 10

PDT WATCHES/WARNINGS/ADVISORIES

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