The National Weather Service’s Portland office issued a flood watch to be in effect from 4 a.m. Monday until 4 a.m. Friday for portions of west-central Oregon, including Benton County.
A prolonged atmospheric river is expected to bring periods of heavy rain to northwest Oregon Monday through Wednesday, with periods of lighter rain continuing Thursday into Friday.
Rivers draining the coastal mountains and several Willamette tributaries have the highest chance of flooding at 40% to 80%. Chances for flooding along the Willamette mainstem remain low at less than 10%.
A forecast for Philomath, as of Sunday afternoon, predicts rain Monday through Wednesday with mostly cloudy conditions Thursday and Friday before rain arrives again over the weekend.
Marys River flow data predicts that it will not reach flood stage — which is considered to be 20 feet — with a crest of 16.99 feet within the period of the flood watch (overnight Wednesday). As of 1 p.m. Sunday, U.S. Geological Survey data showed the river level at under 7 feet.
“Excessive runoff may result in flooding of rivers, creeks, streams and other low-lying and flood-prone locations,” the National Weather Service said through a flood watch alert. “Landslides and debris flows are possible during this flood event. People, structures and roads located below steep slopes, in canyons, and near the mouths of canyons may be at serious risk from rapidly moving landslides.”
Urban flooding is possible and water on roadways will increase the risk of hydroplaning. Landslides in areas of steep terrain will be possible, as well as debris flows over recently burned areas.
Residents in areas that are prone to flooding are advised to be prepared to take action should flooding develop.