textproduct: Pendleton

KEY MESSAGES

- Breezy afternoon winds today and Thursday.

- Warming and dry conditions persist through workweek.

- Precipitation chances return over the weekend.

DISCUSSION

Current radar and infrared satellite imagery shows light showers lingering across the Blue Mountains and foothills under partly cloudy skies. This is a result of a slow moving cold front that will be departing to the southeast by mid-morning, opening the door to surface high pressure moving onshore and into the area. These two features will create a pressure gradient along the Cascades and the Blue Mountains to provide breezy winds across the east slopes of the Washington Cascades, Blue Mountain foothills, and the Lower Columbia Basin both today and Thursday. Sunny skies across the Columbia Basin will enhance these gradients by allowing for surface low pressure to develop as temperatures warm. As a result, winds will peak early to mid- afternoon with gusts of up to 40 mph. This pattern will continue on Thursday as warmer Basin temperatures, stronger surface pressure west of the Cascades, and an upper level ridge building offshore provides a better chance of more widespread wind gusts of up to 40 mph. The most concern resides along the east slopes of the Washington Cascades and the Kittitas Valley, as downsloping winds will be enhanced by the pressure gradient and surface low developing in the Basin during the afternoon. The NBM advertises a 50-70% chance of 35 mph gusts today across the Blue Mountain foothills, east slopes of the Washington Cascades, and Simcoe Highlands, with a 50-80% chance that extends into the Lower Columbia Basin on Thursday. There a low chance of these gusts reaching advisory level (45 mph gusts or greater) as the NBM suggests a 20-35% chance of occurrence over the Simcoe Highlands and Kittitas Valley today and a 20-35% chance over the Simcoe Highlands and the Lower Columbia Basin on Thursday.

The elongated upper level trough extending off the British Columbia/Washington coasts that has been funneling moisture into the area via southwest flow has been cut off and upper flow has now shifting from the northwest associated with the passing of a cold front earlier this morning. This will usher in high pressure as an upper level ridge builds offshore through the remainder of the workweek. Near normal high temperatures are expected today, peaking in the upper 40s to low 50s across the Columbia Basin, Blue Mountain foothills, and Central Oregon. Temperatures will continue to increase each day, eventually approaching the low 60s on Friday. Under this regime, conditions will stay dry and afternoon humidities will drop to between 20-30% across Central Oregon both Thursday and Friday.

Ensembles are in good agreement with the next chance of precipitation returning Saturday, with 77% of members keeping any measurable amounts in Central Oregon. In fact, 66% of members showcase rain amounts only reaching between 0.02-0.04". These showers are associated with the cutoff low, that broke off and moved further into the Pacific this morning, rejoining the flow and approaching the Washington/Oregon coasts early in the weekend. The strength of this low/troughing feature and how strong the incumbent ridge becomes through the remainder of the workweek will determine rain amounts and extent on Saturday. Guidance is trending drier, however both the ECMWF and GFS AI ensembles have suggested a slightly stronger low/trough feature that would further enhance southwest flow and moisture transport over recent model runs. Thus, there still is uncertainty in specific rain amounts and how much they will extend north into northern Oregon and southern Washington, but concerns are minimal as snow levels will hover between 5500-6500 feet. This low/trough feature passes to our east Tuesday as an upper level ridge follows in its wake to bring another dry and warm period to the area. High temperatures may reach into the low 60s Tuesday as the NBM advertises a 70-90% chance of occurrence across Central Oregon, 60-80% chance through the Blue Mountain foothills, and a 35-45% chance over the Tri-Cities area. 75

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

VFR conditions at most sites, with the exceptions being MVFR at KBDN and LIFR at KALW due to reduced ceilings of 2600 feet and 200 feet respectively. Conditions are expected to improve through the morning as ceilings lift due to incoming high pressure. However, the incoming high pressure will result in gradients setting up across the Cascades and Blue Mountains, promoting breezy afternoon winds at KPSC/KDLS/KPDT/KALW with gusts of around 25kts. Winds will subside through the evening and drop to below 10 kts at all sites under VFR conditions. 75

Preliminary Point Temps/PoPs

PDT 29 53 32 56 / 0 0 0 0 ALW 33 53 36 55 / 0 0 0 0 PSC 31 55 34 57 / 0 0 0 0 YKM 27 51 30 53 / 0 0 0 0 HRI 30 55 32 58 / 0 0 0 0 ELN 28 47 31 47 / 10 10 10 10 RDM 21 52 24 58 / 0 0 0 0 LGD 26 51 27 56 / 0 0 0 0 GCD 24 50 28 55 / 0 0 0 0 DLS 31 52 34 55 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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