Weather models predict Oregon’s record snowpack should melt at a slow and steady pace. Umatilla County emergency manager Tom Roberts hopes that’s the case.
“We’re watching the flood monitors and the hydrological gauges along the tributaries just to try to make sure that if something does happen, we have our foot forward,” Roberts said.
The National Weather Service Advanced Hydrologic Prediction Service pegged the Umatilla River in Pendleton at almost 5.8 feet Wednesday afternoon and estimated it would flow a few inches lower the rest of the week. The flood stage for the river in Pendleton is 12.3 feet, which would result in minor flooding of lowland areas from the Riverside area through Pendleton and to Rieth. The U.S. Geological Survey measures the discharge of the Umatilla River where it enters the Columbia near Umatilla. The discharge Wednesday hit 609 cubit feet per second, about 200 cubit feet more than Tuesday. The average for the date, however, is 846 cubit feet a second.
The USDA Natural Resources Conservation Service reported the snowpack for the Umatilla Basin was 154 percent of normal and the Walla Walla Basin stood at 144 percent of normal. Scott Oviatt, snow survey supervisory hydrologist with the Conservation Service, said the late winter storms also buffed up the water year for the Walla Walla and Umatilla basin to 111 percent of normal. But the depth of snow means spring and summer streamflows in the Umatilla, Walla Walla and Willow basins could reach 140 percent of normal April through September.
The fall and winter were warm and dry, he said, but arctic air hit Oregon the second week of February and the jet stream shifted to deliver Pacific moisture that “resulted in significant snow accumulation,” with snowfall in the Blue Mountains at record or near-record levels. How the snowpack “melts out” during the spring, he said, dictates the potential for streams to flood.
Slow melting means the risk is low. But if a spell of warmer weather brings days with temperatures into the 70s, he said, flooding could result, particularly for tributaries.
The Natural Resources Conservation Service will revise its predictions April 1 and May 1. Oviatt said the agency then will have a better notion for how the snowpack is doing and what effects the melt could deliver.
National Weather Service meteorologist Joe Solomon in Pendleton said the region is starting to warm up, but that is not coming with more rain or snow, which would carry a greater threat of flooding.
“If we have warm temperatures with rain falling,” he said, “that would be the worst-case scenario.”
Instead, temperatures will rise during the days and cool off at night. Stream flows, then, will peak later in the day and ebb during the nights and mornings. Meacham in the Blues, he said, could experience temperatures into the upper 40s and lower 50s, but the nights will chill out to the 20s and 30s.
That cooling is going to help keep the snowpack around and cut down on the potential for floods.
A longer-lasting snowpack also would have an effect on fire season, which often arrives around the Fourth of July. Brett Thomas is the fire staff officer on the Umatilla National Forest, Pendleton, and he said the amount of moisture in the Blue Mountains likely means a delayed start to the fire season.
“When I say delayed, I’m talking a couple of weeks,” he said.
Weather in June plays a significant role in when the fire season starts. Hot days without “humidity recovery” at night, he said, can set the stage for fires, and “episodic events” of lighting storms over the region can provide the spark.
Roberts, the emergency manager, said the snow is lingering from The Dalles on, and even Tuesday the region got a dusting of new snow. Still, he advised those living in flood plains should prepare to mitigate hazards. And when the weather permits, he said, folks living where fire is a threat should clear areas around their homes and property. Those defenses, he said, can make the difference to avoid disaster.