textproduct: Pendleton

KEY MESSAGES

- Breezy winds today, subsiding slightly through week.

- Warming and drying trend intensifies Friday through Monday.

- Fire weather concerns over holiday weekend.

DISCUSSION

Current radar and visible satellite imagery shows isolated thunderstorms across southern Wallowa County under mostly sunny to sunny skies. This is in response to a slowly departing shortwave that will keep these cells developing through the afternoon and early evening. Several cloud pulses have been observed via NLDN and GLD data related to a cell southeast of Joseph, however the ECWMF AI ensemble indicates precipitation water amounts of 0.5-0.6" which is around 100% of normal - so developing storm cells should be accompanied by a wetting rain (>0.10"). This shortwave, coupled with surface high pressure offshore, has allowed for a pressure gradient to develop along the Cascades. This has provided another day of breezy conditions through the Eastern Gorge, Simcoe Highlands, and Kittitas Valleys as sustained west-northwest winds of 15-25 mph with gusts of 35-45 mph are expected. Confidence is high in winds staying below advisory criteria (<45 mph) as the NBM advertises a 15-25% chance of 45 mph wind gusts or greater over the aforementioned areas, and a 35-55% chance of 40 mph wind gusts or greater. Another shortwave moves into the area on Thursday, bringing slightly less breezy winds to these areas as a weaker gradient develops along the Cascades. The weaker gradient is a result of overall broadening of the trough these shortwaves are passing through, which also leads to a shift in flow aloft from the northwest to more from the west.

The shift in flow aloft into Friday will intensify the gradual warming trend that has been experienced earlier in the week. High temperatures will transition from about 5 degrees below normal to 5 degrees above normal Thursday through Saturday due to a shift to southwest flow aloft. Afternoon humidities will also transition into the teens across much of the area on Saturday, with portions of Central Oregon dipping into the single digits. Overnight humidity recoveries will also degrade from good (60-80%) values Saturday morning to poor/moderate (30-50%) Monday morning. These humidity values continue through Tuesday as high temperatures peak in the low to mid-90s across the Columbia Basin, Yakima Valley, Blue Mountain foothills, Grande Ronde Valley, John Day Basin, and Central Oregon. There is a likelihood that these temperatures may trend even higher as 57% of ensemble members suggest higher afternoon temperatures than the current forecast on Monday with 46% of members suggesting warmer temperatures than the current forecast on Tuesday. Even though there is less consensus on Tuesday, these members are 3-5 degrees warmer as 20% hint at triple digits over the Tri-Cities area. Due to these high temperatures, and lack of relief with overnight temperatures of around 60 degrees, Moderate HeatRisk is expected across much of the Columbia Basin, Yakima Valley, and northern Blue Mountain foothills both Monday and Tuesday.

The transition from a breezy weather pattern through Friday to a hotter and drier regime through the weekend, elevated fire weather concerns across the Columbia Basin on Saturday afternoon. Critically low minimum humidity values in the low to mid-teens coupled with sustained west winds of 22-27 mph with gusts up to 35 mph may provide enough concern for fire weather products to be issued over the next 36 hours for the Lower Columbia Basin of Oregon, Fire Weather zone OR691. These parameters materialized in the last 24 hours, so further analysis of this trend will need to be conducted with updated guidance. Stay tuned. 75

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

VFR conditions to prevail through the period. Light winds will prevail through the period, except at site DLS where winds of 12-20kts and gusts up to 28kts will impact the site after 17Z tomorrow. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 46 80 52 84 / 0 0 0 0 ALW 52 81 57 85 / 0 0 0 0 PSC 50 83 54 88 / 0 0 0 0 YKM 50 82 54 87 / 0 0 0 0 HRI 49 82 54 87 / 0 0 0 0 ELN 47 77 50 82 / 0 0 0 0 RDM 37 79 43 85 / 0 0 0 0 LGD 44 80 50 83 / 0 0 0 0 GCD 42 82 48 86 / 0 0 0 0 DLS 52 79 56 85 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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