textproduct: Pendleton

KEY MESSAGES

- Dry and above normal temperatures through the week.

- Breezy and fire weather concerns Friday.

- Weekend rain chances, with mountain snowfall possible.

DISCUSSION

Current radar and visible satellite imagery shows dry conditions under mostly clear skies. This is in response to a building upper level ridge offshore that will keep conditions dry and temperatures slightly cooling through the week as northwest flow aloft enhances. A weak, thermal trough is expected to build along the coast on Wednesday, which will allow for light east winds through the Columbia Basin and Gorge. This thermal trough will strengthen on Thursday to provide breezier winds through the Columbia Gorge, primarily west of the Hood River area. These east winds will keep overnight humidity recoveries in the 30-50% range across portions of Central Oregon, John Day Basin/Highlands, Blue Mountains, Elkhorns, and the Cascade gaps.

The ridge of high pressure shifts further west and into the Eastern Pacific late Thursday to Friday, opening the door to a dropping upper level trough from the Gulf of Alaska. Due to the influence of the departing ridge and incumbent dry air from the east winds Wednesday and Thursday, limited rain is expected as winds will be the primary concern. The GFS and NAM advertise a pressure gradient of 11-12.5 mb over the Cascades, which suggests winds reaching advisory criteria. The NBM showcases a 20-40% chance of sustained winds of 30 mph or greater, with a 30-60% chance of gusts reaching 45 mph or greater across the Simcoe Highlands, Kittitas Valley, and portions of the Columbia Basin on Friday. Afternoon humidities will drop into the teens across the John Day Basin and portions of Central Oregon on Friday, which may lead to isolated fire control and spread concerns as well. These elevated winds may also provide areas of blowing dust, potentially decreasing visibilities and causing travel concerns along the Interstate 90, 84, and 82 corridors.

Guidance is continuing to struggle with the overall strength of the incoming upper level trough on Friday, highlighted by a 73% ensemble member variance in system strength. 60% of ensemble members show a significant system moving through the area during peak afternoon hours on Friday, which aligns with a slight potential for advisories through portions of the Basin. 24% of members also suggest a slightly later passing of the system, alleviating some wind concerns and producing sub- advisory winds. The primary moisture supply for this system is the remnants of Hurricane Rachel as it turns north and transitions to sub-tropical status as the trough strengthens and drops south through the Pacific Northwest. The stronger trough is more efficient at bringing moisture from Rachel's remnants north and across the area, but rain amounts are still rather low and below a wetting rain for most of the region. Currently, 89% of ensemble members show the majority of the area receiving measurable rainfall (0.01" or greater) Saturday, with more widespread measurable rain on Sunday. Regardless of outcome, 48-hour rain amounts look to stay around 0.05" or less across lower elevations, and up to 0.1-0.15" for higher terrain across the Blue Mountains Saturday through Sunday. Snow levels will also be in decline over the weekend, reaching around 3,000 feet on Sunday - so there is also potential for snowfall over higher terrain Saturday night into Sunday morning. A freeze concern is also present across Central Oregon and portions of the Columbia Basin starting Sunday. The NBM advertises a 50-70% chance of freezing temperatures Monday morning across Central Oregon and the Blue Mountain foothills, so freeze products may be warranted. Stay tuned. 75

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

VFR conditions prevail. Winds are variable through most of the region. prevailing winds will be calm and follow typical diurnal patters. Sky cover is light with mostly high base clouds around 25,000FT.

Preliminary Point Temps/PoPs

PDT 46 79 46 80 / 0 0 0 0 ALW 51 80 52 81 / 0 0 0 0 PSC 45 80 46 81 / 0 0 0 0 YKM 49 80 50 82 / 0 0 0 0 HRI 45 80 45 81 / 0 0 0 0 ELN 46 77 49 79 / 0 0 0 0 RDM 41 82 41 83 / 0 0 0 0 LGD 46 84 47 84 / 0 0 0 0 GCD 48 89 49 88 / 0 0 0 0 DLS 52 84 53 85 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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