Umatilla, OR Weather

Discussion

Satellite imagery this afternoon shows an upper closed low spinning away off the coast of CA while a band of mid to upper level cloud cover reaches up into central and northeast OR.

Today through Wednesday: While an upper low continues to sit off the CA coast today, and upper level ridge will slide across northern WA and BC. The forecast area will be under the influence of this upper ridge, resulting in dry conditions, above normal temperatures, and light winds the rest of today. By tomorrow, the upper ridge will be east of the region with south to southwest flow over the forecast area. This will result in continued dry conditions and light winds. To the south, the upper low will begin to swing into central CA, with precipitation ahead of the low reaching southern OR by Wednesday night.

Thursday and Friday: Later this work week, the PacNW will be impacted by two systems: the upper closed low passing to the south and east and upper trough with attendant cold front sliding across the PacNW.

The upper closed low passage will be the main precipitation maker through this period. Showers will begin to develop across the high terrain south and east of John Day Wednesday night, then through Thursday will spread to the remainder of the eastern mountains, central OR, and the eastern half of the Columbia Basin by Thursday afternoon. Shower chances will dissipate from west to east Thursday evening into Friday morning as the upper low continues east of the region. Thursday, 24-hr chances between 75-95% of 0.25 inches of rain are focused around the northern Blue Mountains, Elkhorn Crest, and Wallowa County; along the Blue Mountain foothills and the remainder of the eastern mountains, chances of 0.1 inches are 45-65%. In the remainder of the areas, there is a 30-50% chance of at least 0.01 inches.

The upper trough and cold front passage late Thursday through Friday will bring wind impacts throughout the forecast area. Winds will begin to increase through the Cascade gaps Thursday afternoon, and continue to strengthen overnight as the cold front drags across the intermountain PacNW. Winds are currently expected (confidence 55-70%) to peak overnight Thursday into Friday morning between 25-35 mph with gusts to around 45 mph through the eastern Gorge and Kittitas Valley, while winds will be slightly weaker (20-30 mph with gusts up to 40 mph) in portions of the Columbia Basin, Central OR, Cascade east slopes, and eastern mountains (including Grande Ronde Valley). Breezy winds will carry on into the afternoon Friday, but become light by the nighttime hours.

Lastly, the upper closed low swinging inland will become an open trough with a negative tilt by Thursday afternoon. Ahead of the trough's axis, SBCAPE between 200-250 J/kg will develop across the eastern mountains. Increased CAPE and the negative tilt will result in chances (15-25%) of isolated thunderstorms developing Thursday afternoon.

Aviation

VFR conditions currently across all sites, which will stay the course through the period. Light winds below 7kts are expected to persist, with minimal clouds. KRDM and KBDN will experience more BKN/SCT cloud cover at 25kft. 75

Pdt Watches

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