textproduct: Pendleton

KEY MESSAGES

- Above normal temperatures and dry through Thursday.

- Breezy winds with isolated fire weather concerns Friday.

- Chilly morning temperatures and rain chances over the weekend.

DISCUSSION

Current radar and visible satellite imagery shows dry conditions under clear skies. This is a result of an upper level ridge located just offshore. The ridge will begin to track west and further into the Eastern Pacific into Thursday, opening the door to an incoming system originating from the Gulf of Alaska late in the week. The approaching system will shift winds aloft from the northwest to more from the west on Thursday to allow for a slight 2 to 4 degree increase in high temperatures. Highs will peak in the low to mid-80s across Central Oregon and over the majority of the Columbia Basin. A weak thermal trough will also develop on Thursday, helping to further warm temperatures and dry conditions as afternoon humidities dip into the mid-teens across Central Oregon and low-20s across lower elevations of the Columbia Basin.

The approaching system will allow for a pressure gradient to develop along the Cascades on Friday, as advertised by a 11-13 mb gradient between Portland and Spokane via the GFS, NAM, and SREF. This would relate to sustained west-northwest winds of 23-28 mph with gusts of 35 to 45 mph across the Simcoe Highlands, Columbia Gorge, and Blue Mountain foothills. Currently, the NBM suggests the best chances for advisory level winds (Gusts of 45 mph or greater) occurring across the Simcoe Highlands at a 60-70% chance, compared to a 30-40% chance over the Blue Mountains foothills, and a 20-30% chance through the Kittitas Valley. Peak winds are expected between 2PM and 8PM. These elevated winds, coupled with the dry, incumbent air may lead to isolated fire control concerns - especially over areas of Central Oregon and Northern Wallowa county. Another, more widespread concern also arises under these conditions - blowing dust. There is a potential for reduced visibility as a result of blowing dust, which could occur across the Columbia Basin, Columbia Gorge, and the Yakima/Kittitas Valleys on Friday. Visibilities as low as one mile is possible, and may change quickly due to the passing cold front.

Frigid temperatures are anticipated Saturday onward as north flow aloft efficiently funnels cold, arctic air into the region from northern British Columbia, Northwest Territories, and Yukon provinces. This incoming airmass will lead to freeze potential for Central Oregon and Wallowa County Saturday morning, becoming more widespread Sunday and Monday morning across the Columbia Basin. Guidance still struggles with the upper level trough's strength, which directly relates to how efficient cold air advects into the area from the north. Currently, 52% of ensemble members advertise a stronger system, which leads to a colder scenario both Sunday and Monday mornings. A stronger system would also better tap into moisture associated with the remnants of Hurricane Rachel as it progresses north and transitions to post-tropical status. Overall, rain amounts are expected to be limited to around 0.05" for lower elevations and a wetting rain for the Cascade and Blue mountains. The colder incoming air will also decrease snow levels to between 3000 and 4000 feet, bringing the first one to two inches over the Elkhorns. A light dusting is likely over the Blues, Cascades, and John Day Highlands Saturday night through Monday morning, with 88% of ensemble members aligning with this outcome. 75

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

VFR conditions are forecasted throughout the TAF period. Generally, winds will be light at 10 kts or less. There are no CIG or VIS concerns for the next 24 hours.

Preliminary Point Temps/PoPs

PDT 46 80 50 72 / 0 0 0 0 ALW 52 81 56 72 / 0 0 0 0 PSC 46 82 48 75 / 0 0 0 0 YKM 50 81 50 70 / 0 0 0 0 HRI 45 81 49 73 / 0 0 0 0 ELN 48 79 49 63 / 0 0 0 0 RDM 40 82 41 71 / 0 0 0 0 LGD 46 83 47 74 / 0 0 0 0 GCD 48 86 47 76 / 0 0 0 0 DLS 53 85 53 70 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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