textproduct: Pendleton

KEY MESSAGES

- Mountain snow showers continue through this evening

- Slight chance of thunderstorms this afternoon, mainly Columbia Basin and Blue Mountain foothills

- Mostly dry and warming conditions Monday through Friday

DISCUSSION

Scattered showers and isolated thunderstorms have developed across the forecast area today as the combination of daytime heating and cooler temperatures aloft under an upper-level low have facilitated steepening low- and mid-level lapse rates. Best chances (15-25 percent) of thunder will be across the lower Columbia Basin and along the Blue Mountain foothills this afternoon and evening, with lower (10-15 percent) chances for the Cascades and Blues of northeast Oregon and far southeast Washington. Small hail, gusty outflow winds, and cloud-to-ground lightning constitute the main hazards with thunderstorms today. Loss of daytime heating should put a damper on the more robust convection by late evening, but forcing from a shortwave rounding the base of the upper low should keep mountain snow showers going into the overnight hours (80 percent confidence). Additional snow accumulations of a trace to several inches are forecast for the Cascades and Blue Mountains this evening into the overnight hours.

Widespread breezy to windy westerly winds this afternoon have flirted with advisory criteria for portions of the lower Columbia Basin, eastern Columbia River Gorge, and Blue Mountain foothills, but confidence in sustained advisory criteria across a broad enough region was too low (50 percent) to warrant the issuance of any wind headlines. Winds will slacken overnight.

While no headlines for freezing temperatures have been issued, there is low (10-40 percent) confidence in near- to sub-freezing morning lows in the Yakima and Kittitas valleys, lower Columbia Basin, and Blue Mountain foothills Sunday morning. Elsewhere, confidence is higher (40-60 percent) for the Grande Ronde Valley, Simcoe Highlands, and north-central Oregon. Have included a mention of frost in the forecast for the aforementioned areas for messaging. Should cloud cover clear more quickly than forecast this evening, and winds slacken earlier than anticipated, temperatures will have the potential to drop below what is forecast.

Monday through Friday, warming temperatures and mostly dry conditions are forecast region-wide as an upper-level ridge of high pressure will likely (80-90 percent chance) dominate the weather. A couple weak shortwaves passing through northwesterly flow aloft may facilitate some showers for the mountains, but PoPs are low (generally 5-15 percent, except 15-25 percent for the northern Blues on Monday). The alternate, less-likely scenario (10-15 percent chance per 12Z ensemble cluster analysis) is for a closed low to dive south from Canada and place the region under cool, showery weather between Wednesday and Thursday.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Widespread showers and isolated thunder storms continue through the region. Expecting convection coverage to decrease as we get closer to sunset hours, so not expecting any thunderstorm impacts at the sites (although PSC has a small 5 to 15% chance of a passing storm through 03Z). Majority of the rain will move out of the area by 03Z, with mostly dry conditions by 06Z. Some of these showers can bring gusty 20-30 knot gust with temporary MVFR conditions developing (5 to 15% chance). VFR conditions expected over the next 24-hours, except for the small chance mentioned earlier.

Preliminary Point Temps/PoPs

PDT 36 62 39 69 / 30 10 0 0 ALW 40 62 42 69 / 50 10 0 0 PSC 38 70 41 75 / 20 0 0 0 YKM 37 71 41 74 / 0 0 0 0 HRI 36 68 40 73 / 20 0 0 0 ELN 34 64 38 68 / 0 0 0 0 RDM 26 60 28 68 / 20 0 0 0 LGD 33 54 33 64 / 60 10 0 0 GCD 31 54 31 65 / 60 10 0 0 DLS 39 67 43 73 / 10 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 11 PM PDT this evening for WAZ522. OR...Winter Weather Advisory until 11 PM PDT this evening for ORZ509.