textproduct: Pendleton

KEY MESSAGES

- Cold air mass expected to move through the area this weekend and next week

- Breezy conditions this weekend along the Eastern Oregon Cascades, Washington Cascades, Lower Columbia Basin and Yakima Valley

- Return of mostly dry conditions, light winds, and above normal temperatures middle of next week

DISCUSSION

Scattered to broken cloud layers around 6000 ft were common across the forecast area This Afternoon with of more sun through the Columbia River Gorge and southeast Washington. A zonal flow pattern was giving way to a mid level troughing of cooler air aloft over the PAC NW that will continue to amplify through Monday Night into the Great Basin. Challenging forecast in terms of where the cold air will have impacts. There is a large discrepancy in the short term ensemble models and the NBM's more weighted raw inputs and bias corrected member data having very cold air the the 20s across the Wallowa Valley overnight. HREF shows a more muted temp trend as cloud cover, which kept temps in the the mid 30 last night again shows its hand overnight not only in the total cloud cover but in low level HRRR fields between about midnight and 14z (increasing trends). The uncertainty lies in the cloud cover; if any appreciable clearing occurs or the clouds fail to redevelop, colder sub freezing temperatures could will develop quickly. At this time, forecaster confidence doesn't reach the thresholds to continue freeze warnings in the very near term. With Redmond and Bend reaching 32 and colder last night, the central Oregon forecast zone is now being considered as having its season-ending freeze. Showers across the Wallowas are also possible Sunday night as the NBM is putting in fairly high pops in the 50 to 70% range over these high elevations. Monday night and Tuesday morning may present the same issues with cloud cover across a larger area with respect to freeze headlines. There is a ensemble member trend where the cloud cover is clearing out better across the western zones, if not Monday morning across the northwest, certainly by Tuesday morning, over the entire area. North Central Oregon, some of the Foothills of the Blues and northward into the Kittitas and Yakima valley areas should be prone to freezing by Tuesday morning. Kittitas Valley already has an 80% chance from NBM members of reaching below 32 degrees for Monday morning, coincident with high confidence in clearing sky and a freeze watch is being hoisted for that zone.

Once the upper low/trough moves through the region Tuesday, temperatures begin a sharp rebound as afternoon highs rise out of the 60s and back into the 70s for the Columbia Basin and River Gorge, for the latter half of the week. Corresponding "not as cold lows" in the upper 30s and lower to mid 40s are the NBM's favored temps for non mountain zones.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

VFR conditions are forecast at all sites through this evening, albeit with FEW-BKN clouds ~4-7 kft AGL. Aside from breezy westerly winds at DLS, and periodic gusts elsewhere, light winds of 10 kts or less are forecast into tonight. North to northeast winds will increase in magnitude at for all sites Sunday.

Chances of MVFR CIGs/VSBYs increase later tonight into Sunday morning, mainly at BDN/RDM where 12Z HREF probabilities are 50-90% for MVFR CIGs and 10-40% for MVFR VSBYs, and 12Z REFS probabilities are 40-60% for MVFR CIGs and <10% for MVFR VSBYs Sunday morning. Elsewhere, chances of MVFR conditions are low (20% or less).

Preliminary Point Temps/PoPs

PDT 38 54 31 57 / 0 10 10 10 ALW 40 55 35 57 / 0 10 10 10 PSC 44 60 35 62 / 0 10 0 0 YKM 42 59 34 63 / 20 10 0 0 HRI 41 58 34 61 / 0 10 0 0 ELN 38 55 29 60 / 40 10 0 0 RDM 32 48 22 55 / 0 10 0 0 LGD 35 50 31 55 / 0 10 20 10 GCD 29 50 29 55 / 0 0 10 10 DLS 45 63 38 67 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Freeze Watch from Sunday evening through Monday morning for WAZ026. OR...None.