textproduct: Pendleton

KEY MESSAGES

- Periodic shower chances (35-85%) across the mountain zones will continue through the weekend, with lower chances in the lower elevations

- Isolated thunderstorm chances (15-25%) will develop across Cascades, Blues, and Wallowa county Today and Friday

- Below normal temperatures through early next week, with potential for freezing temperatures in mountain valleys tonight and Friday night

DISCUSSION

Water vapor satellite imagery tonight shows a shortwave trough lifting northeast across the intermountain PacNW, while an upper low offshore is swinging southeast towards the coast. The shortwave trough passage this morning has resulted in light to moderate rainfall continuing across the eastern half of the forecast area. This activity will diminish in the lower elevations over the next couple of hours as the shortwave lifts into ID, with light showers continuing across the mountains.

Today through this weekend, the PacNW will be under the influence of the upper level low currently offshore, with another couple rounds of rain showers in the lower elevations, with more persistent chances across the mountains (confidence 70-90%). Temperatures across the region will be nearly 10-15 degrees below average each day, with afternoon high temperatures at their lowest in the mid 60s and low 70s today and Friday (confidence 80-90%). By this afternoon, the upper closed low will park itself over the PacNW, with the center of the low remaining west of the Cascade crest through Saturday before sliding east Sunday into Monday(confidence 75-85%). During this time, persistent rain shower chances (30-60%) will remain over the Cascades and eastern mountains each day, with shortwave impulses Friday/Saturday and the low passage Sunday/Monday producing light rain chances (15-40%) in the lower elevations. Isolated thunderstorms will be possible over the mountains today and Friday as weak instability develops in these areas with additional support from the cold core of the low aloft. As for precipitation amounts, the Cascades and Blues will see 0.1 to 0.25 inches of daily precip (confidence 70-90%), with locally higher amounts where thunderstorms develop.

Sunday into Monday, ensemble and deterministic members show the upper closed low beginning to push east, with the low over the forecast area during the day Sunday. While light to moderate rain showers are forecast across the area, the upper low being overhead and weak instability developing will also result in slight chances (15-25%) of isolated thunderstorms focused across central OR and the eastern mountains Sunday afternoon and evening. By Monday evening, what is left of the upper level low will have pushed east of the region, with showers diminishing area wide.

Tuesday and Wednesday, ensemble members are in good agreement of weak split flow developing over the PacNW as weak zonal flow develops to the north and troughing to the south. This will result in mostly dry conditions, light winds, and near normal temperatures across the region (confidence 40-50%). Lawhorn/82

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

An upper low will continue bringing rain showers and isolated thunderstorms through the TAF period to the mountian zones. Most of the cloud ceilings will be in the the VFR to MVFR range, with about a 20% chance for IFR (2-3kft) cigs in rain showers in the Blue Mt foothills (ALW/PDT) overnight. Winds under 12 kts.

Preliminary Point Temps/PoPs

PDT 68 42 69 42 / 10 40 40 30 ALW 69 47 70 47 / 30 50 40 20 PSC 73 45 73 45 / 0 20 20 10 YKM 70 48 71 48 / 10 10 20 20 HRI 71 45 72 45 / 0 20 20 20 ELN 66 42 67 42 / 30 10 40 30 RDM 64 33 64 34 / 10 50 60 50 LGD 66 42 67 42 / 80 90 50 40 GCD 63 40 67 41 / 80 90 40 50 DLS 70 50 74 51 / 30 40 20 30

PDT WATCHES/WARNINGS/ADVISORIES

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