PORTLAND, Ore. – A stream of atmospheric rivers will be flowing through parts the Pacific Northwest at the beginning of December, drastically changing the region’s most recent crisp, dry autumn – a seemingly strange occurrence. The National Weather Service’s (NWS) Portland office is predicting that up to three atmospheric rivers will pummel the region, bringing a very active weather pattern that will dump plenty of rain at lower elevations and snow to the Cascades.
The NWS’ forecast discussion mentions there is some uncertainty with the prediction but to expect rain, snow and wind. It continues, “aside from dangerous travel conditions over the Cascade passes during this time, flooding concerns will begin to increase along rivers, creeks, small streams, and in urban areas with poor drainage as river levels will already be elevated leading into the second round of heavy precipitation.”
Predictions, which are based off models, and events like this captivate the staff in Northwestern Division’s Reservoir Control Center (RCC), as they must monitor and prepare to adjust operations at U.S. Army Corps of Engineers (USACE) and Bureau of Reclamation dams. Both federal agencies work together to reduce flooding on the mainstem dams in the Columbia River Basin. These agencies also work with entities in Canada, other dam operators, the Bonneville Power Administration (BPA) and fish managers during storm events.
Catherine Dudgeon, hydraulic engineer and water regulator for the RCC, is responsible for tracking this particular weather event.
“In general, I don't feel worried or stressed,” said Dudgeon. “I'm actually hoping that a lot of this precipitation gets soaked into the ground and hopefully this could help with the snowpack which is important for next spring,” she said. “With that being said, all models are wrong, some are useful. Sometimes we have to wait to see what we get.”
At this point, the RCC doesn’t anticipate adjusting operations on the Columbia River because most of the rain will be beneficial since conditions have been dry throughout the basin. Most storage projects in the basin have some reservoir space to store water, if needed. Aaron Marshall, acting RCC chief, anticipates that the most significant impacts will be for western Washington, primarily on unregulated rivers and streams.
“However, these atmospheric river events are very unpredictable, so we'll track it and adjust operations if needed,” said Marshall. “Portland District will be making some adjustments at the Willamette Valley projects, but even there we aren't seeing any control points forecast to reach flood stage with this event,” he said. “It's important for people to remember that these atmospheric river events are difficult to forecast with much confidence and that small streams and rivers can be flashy and rise very quickly. For travelers, we are expecting heavy wet snow in the Cascades that will make for dangerous driving conditions.”
Dudgeon won’t be alone, as other members of the RCC will be watching the weather system throughout the weekend and supporting as needed.
“Between our Reservoir Regulation team at Division, we also have the districts, BPA and Reclamation as partners to help lean on during flood events,” said Dudgeon. “It really is a team effort!”
For now, the NWS is forecasting the Columbia River at Vancouver to remain below eight feet (flood stage is 16 feet), so water regulators don’t anticipate needing to implement flood risk management actions. However, the RCC would adjust the reservoir at Grand Coulee Dam in northeast Washington, first. Then, they would modify John Day Dam’s reservoir next if they started seeing potential for Vancouver to reach flood stage.