textproduct: Pendleton

KEY MESSAGES

- Warm and dry conditions persist through the week.

- Incoming system Friday brings breezy to windy conditions.

- Pattern shifts to cooler and wetter over the weekend.

DISCUSSION

current radar and visible satellite imagery shows dry conditions under mostly clear skies. This is in response to an upper level ridge that will strengthen across the Eastern Pacific through much of the week. High temperatures peak today, reaching into the mid-to upper 80s across the Columbia Basin and Central Oregon. A weak upper level shortwave will dissipate as it moves into the area from the northwest, enhancing winds slightly through the Columbia Gorge and across the Kittitas Valley. Wind gusts of 33 mph have already been recorded at Ellensburg, with gusts expected to peak around 5PM up to 38 mph. Winds over the Columbia Gorge will also be on the rise, with gusts up to 35 mph possible at The Dalles. Flow aloft becomes more from the northwest in the wake of the passing shortwave on Tuesday and Wednesday. This allows high temperatures to dip into the upper 70s to low 80s both days. A slight increase in high temperatures is likely Thursday, in association with a building thermal trough along the Oregon coast. This synoptic feature will lead to winds being from the east across the Columbia Basin, dropping afternoon humidities into the low to mid-20s on Thursday. A weak thermal trough does develop on Wednesday which keeps overnight humidity recoveries into Thursday morning around 40% across areas of the John Day Highlands, Northern Blue Mountains, and Central Oregon.

The upper level ridge slides west and further offshore on Friday, opening the door to a dropping upper level trough that originates in the Gulf of Alaska. This trough will approach the Washington-Canadian border early Friday morning before moving over the region and strengthening south into Northern California over the weekend. The arrival of the trough will lead to breezy winds across much of the area, as indicated by an 11-12 mb pressure gradient between Portland and Spokane via the GFS. This gradient aligns with near advisory-level values, but at this time the NBM only advertises a 15-30% chance of wind gusts reaching 45 mph or higher. The trough continues to strengthen and dig south on Saturday, interacting with the remnants of Hurricane Rachel as it turns north and becomes subtropical. This influx of moisture is still rather minimal, with 33% of ensemble members keeping the area dry on Saturday, and 67% of members bringing only 0.01-0.04" of rain to higher elevations. These differences are a result from guidance either bringing in the through (highly advertised by the ECMWF) or keeping the ridge or zonal pattern (suggested by the Canadian and GEFS). However, it is important to note that both the AI ECMWF and GEFS ensembles showcase a troughing scenario. Sunday is currently expected to be the wetter day this weekend, but rain amounts still struggle to reach wetting rain amounts. 75

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

With high pressure remaining over the area throughout the period, VFR conditions will persist. Winds will generally remain below 12kts throughout the period and direction is diurnally terrain driven. Garty/26

Preliminary Point Temps/PoPs

PDT 47 79 46 79 / 0 0 0 0 ALW 54 80 51 80 / 0 0 0 0 PSC 49 80 45 80 / 0 0 0 0 YKM 50 79 49 80 / 0 0 0 0 HRI 50 81 45 80 / 0 0 0 0 ELN 47 77 46 77 / 0 0 0 0 RDM 43 84 41 82 / 0 0 0 0 LGD 46 83 46 84 / 0 0 0 0 GCD 48 85 48 88 / 0 0 0 0 DLS 52 84 51 84 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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