textproduct: Pendleton

KEY MESSAGES

- Warmer day today, slight cooling through the weekend. *Heat Advisory Active*

- Dry and breezy through Saturday, lower winds next week.

- Elevated fire weather concerns through Saturday.

DISCUSSION

Current radar and infrared satellite imagery shows dry conditions under clear skies. This is in response to a building upper level ridge to our southeast, keeping skies clear and conditions dry. Enhancing today's warming will be a dropping upper level low pressure along the British Columbia coast, that will shift flow aloft from the west to the southwest during the day.These features will allow high temperatures to reach into the low to mid-90s across the Lower Columbia Basin, Blue Mountain foothills, Central Oregon, John Day Basin, and Yakima Valley. Excessive heat is expected through the Hells Canyon area as high pressure dominates from the southeast and advects a more dry, continental airmass across far Eastern Oregon. Daily high temperatures of up to 105 will be possible with widespread moderate HeatRisk (2 out of 4). These conditions have warranted the issuance of a Heat Advisory for the Hells Canyon area below 3000 feet from noon today through 7 PM Sunday. If in this area over the next 72 hours, make sure to stay hydrated and take precautions from the heat. Isolated areas of moderate HeatRisk will be present today over the Basin and foothills, primarily over the Yakima, Hanford, and Walla Walla/Milton Freewater areas. The upper level low offshore will continue to drop near Vancouver Island Saturday before moving inland on Sunday, which will bring slightly cooler conditions across the Columbia Basin coupled with a slight uptick in moisture due to the associated maritime airmass.

The approaching upper level low offshore and the building upper level ridge to the southeast will tighten the pressure gradient between these two features. West-northwest winds of 20-25 mph with gusts of around 35 mph are expected across the Columbia Gorge, Southern Blue Mountain foothills, and the Kittitas Valley, with 10-20 mph winds and gusts around 25 mph over the Lower Columbia Basin, Northern Blue Mountain foothills, and the Yakima Valley. These winds are forecast to peak between 5 PM and 8 PM today, as an embedded shortwave moves through the southwest flow aloft. In the wake of its passing, upper level ridging will infiltrate from the southeast to confine these breezy conditions to the Eastern Gorge, Simcoe Highlands, and the Cascade gaps/east slopes on Saturday. The upper level low rides up and over the ridge through Central Canada on Monday to allow the ridge to strengthen across the area and lower winds Sunday onward. The continued presence of the strong high pressure to our southeast keeps conditions dry until Monday/Tuesday (15% chance) as both the ECMWF AI ensembles and GFS AI ensembles advertise a passing shortwave may bring increased moisture across Central and Eastern Oregon - as well as isolated thunderstorm chances.

The more widespread winds and low afternoon humidities dropping into the mid-teens elevates fire weather concerns today, primarily between 3 PM and 7 PM across the Eastern Gorge and the Warm Springs areas. Elevated concerns return briefly Saturday across the Yakima Valley, as winds decrease Sunday onward to alleviate these concerns into next week. 75

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

VFR conditions are expected through Saturday. Gusty winds will continue at DLS, where wind gusts to 25 kts are expected both today and Saturday. At PDT, RDM and BDN, wind gusts are to around 25 kts are expected this afternoon and evening with lighter winds on Saturday. Elsewhere, winds should be 10 kts or less.

FIRE WEATHER

Most fire weather concern occurs today between 1500 and 1900 across fire weather zones WA691, OR691 and OR703, but stay primarily along the western borders of the WA/OR691 zones and eastern border of OR703. The NBM highlights highest chances of critical humidities and winds being met around the Arlington/Ione areas at a 40-60% chance at 1700. Even more isolated concerns are expected Saturday over the western portion of WA691 between 1700-1900 with a 40-50% chance of occurrence.

Conditions will stay dry next week with moderate humidity recoveries between 35-50% across the Columbia Basin, Blue Mountains, and Central Oregon, with afternoon humidities between 15-25% each day. The limiting factor will be the lack of wind due to the upper level high to our southeast dominating the weather pattern. The incoming shortwave Monday and Tuesday may allow for isolated thunderstorms across OR693-700 and OR705 zones, but currently confidence is low (10-15%). 75

Preliminary Point Temps/PoPs

PDT 90 56 87 57 / 0 0 0 0 ALW 93 62 90 62 / 0 0 0 0 PSC 95 60 92 61 / 0 0 0 0 YKM 94 57 90 58 / 0 0 0 0 HRI 93 60 90 60 / 0 0 0 0 ELN 87 54 83 52 / 0 0 0 0 RDM 89 47 88 52 / 0 0 0 0 LGD 94 55 95 57 / 0 0 0 0 GCD 96 54 97 56 / 0 0 0 0 DLS 88 59 85 60 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Heat Advisory until 7 PM PDT Sunday for ORZ050.