textproduct: Pendleton

KEY MESSAGES

- Breezy afternoon winds today and Friday.

- Dry and warming through the workweek.

- Next chance of precipitation returns over the weekend.

DISCUSSION

Current radar and infrared satellite imagery shows dry conditions under clear skies. This is in response to the upper level ridge building just offshore to allow for surface high pressure to push onshore and through the Pacific Northwest. Another sunny day expected across the Columbia Basin today, leading to pressure gradients returning across the Cascades to allow for breezy winds to develop across the east slopes of the Washington Cascades, Simcoe Highlands, Blue Mountain foothills, Lower Columbia Basin, and the Yakima/Kittitas Valleys this afternoon. Developing surface low pressure over the Columbia Basin, as a result of clear skies and efficient warming due to downsloping dry air, will also help to enhance the pressure gradient - especially through the Kittitas Valley and the Simcoe Highlands. This will lead to wind gusts of up to 40 mph this afternoon across these zones, with 25-35 mph gusts expected through the Lower Columbia Basin and Blue Mountain foothills. Ellensburg did briefly experience Advisory-level gusts (46 mph gust around 1 PM) yesterday, but the absence of a departing frontal system should relax the pressure gradient enough to keep gusts sub-advisory this afternoon. Friday's winds may be a different story, as an upper level trough and cold front pass through British Columbia and may enhance the pressure gradient over the Cascades. This is evident in the NBM's analysis with advisory wind gusts being achieved with the 95th percentile (1 in 20 chance) today and the 90th percentile (1 in 10 chance) on Friday for Ellensburg. In comparison, yesterday's 07z NBM run suggested advisory-level winds (45 mph or greater) at Ellensburg at the 90th percentile.

The presence of the upper level ridge will keep skies clear and temperatures warming through Friday. High temperatures are expected to reach into the mid-to upper 50s today and the upper 50s to low 60s Friday across the Lower Columbia Basin, Blue Mountain foothills, and Central Oregon - which is about 5 degrees warmer than normal. These warmer conditions, coupled with downsloping and dry winds, will lead to afternoon humidities across Central Oregon, Blue Mountain valleys, north- central Oregon, and portions of the Columbia Basin dropping to between 15-30% both today and Friday. Moderate to good (40-65%) overnight humidities are anticipated through the workweek, with Friday being the drier day as the upper level ridge moves onshore.

The upper level low pressure that cutoff from the overall flow and put a halt to showers earlier in the week will return as a weakening system over the weekend. This will bring precipitation across Central Oregon Saturday through Sunday morning. As anticipated in Wednesday morning's discussion, precipitation amounts have trended upwards (0.01-0.06" up from 0.01-0.02" 24 hours ago) and extent has pushed slightly further north to include portions of the John Day Basin and the Bend/Redmond areas. These trends were evident in the increasing strength of the incoming upper level low via the ECMWF and GFS AI ensembles, which is still prevalent in the ECMWF AI ensembles. LREF ensemble clusters have also alluded to this as 87% of members now bring measurable rainfall (0.01" or greater) into portions of Wallowa and Union counties on Saturday. This may continue to trend in this direction in subsequent model runs, but with the lack of overall consistency in AI ensembles (GFS weakening incoming system from previous runs) the trend is likely to slow. Regardless, overall impacts will be minimal as snow levels will hover between 4500-6500 feet both days.

High pressure returns Monday in the wake of the passing weekend system, bringing dry and warm conditions back to the area as highs peak in the upper-50s to low-60s across Central Oregon, Blue Mountain foothills, and the Lower Columbia Basin on Tuesday. Guidance is in good agreement with a more substantial upper level trough and associated cold front passing through the Pacific Northwest on Wednesday, with 82% of LREF ensembles showcasing widespread precipitation. Snow levels look to drop to between 4000-5000 feet on Wednesday, allowing for our mountain zones to pick up 1-3 inches. Confidence in these snow amounts is currently low (20-30%) as overall strength of the incoming system is still in question (56% of ensemble members hint at stronger system that current forecast). Stay Tuned. 75

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

VFR conditions currently across all sites, which will stay the course through the period. Winds will increase through the morning and peak through the afternoon as values between 10-15 kts are likely at KPSC/KALW/KPDT/KDLS. Elsewhere, winds should stay below 10 kts. 25kft FEW-SCT ceilings will develop through the afternoon across all terminals, clearing through the evening. 75

Preliminary Point Temps/PoPs

PDT 31 56 32 50 / 0 0 0 0 ALW 35 55 35 51 / 0 0 0 0 PSC 32 57 31 52 / 0 0 0 0 YKM 29 53 31 50 / 0 0 0 0 HRI 31 57 31 52 / 0 0 0 0 ELN 30 48 30 48 / 0 0 0 0 RDM 25 58 28 54 / 0 0 0 10 LGD 29 56 31 54 / 0 0 0 10 GCD 28 55 32 55 / 0 0 0 10 DLS 33 55 33 52 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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