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 /12Z TAFS THROUGH 12Z FRIDAY/

VFR conditions to prevail through the period. Upper level low pressure system impacting the region will produce a chance (25-35%) of light rain showers at most sites between 22Z-06Z, except at sites YKM/PSC where chances are much lower through the period. CIGs may lower down to around 5kft with precipitation, with vsby remaining above 6 miles in precipitation. Winds will be light, 12kts or less, through the period. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 68 42 68 43 / 10 40 30 10 ALW 69 46 68 47 / 20 40 30 20 PSC 73 43 73 43 / 0 10 20 10 YKM 70 45 71 47 / 10 10 20 10 HRI 71 43 71 43 / 0 20 10 20 ELN 66 40 66 41 / 30 20 40 20 RDM 64 31 63 32 / 20 40 50 60 LGD 66 41 66 39 / 80 80 60 40 GCD 63 39 65 39 / 80 70 40 30 DLS 70 47 72 48 / 30 30 20 30

PDT WATCHES/WARNINGS/ADVISORIES

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