The National Weather Service’s Portland office has issued a flood watch for Benton County and portions of northwest Oregon and southwest Washington, effective from 4 a.m. Thursday through 4 a.m. Saturday.
An atmospheric river is forecast to bring periods of heavy rain to the region at a time when area rivers continue to run high and soils remain saturated following heavy rain earlier in the month, officials said.
In addition to Benton, the flood watch covers 13 other Oregon counties and five Washington counties.
According to the weather service, the urban and small stream flooding threat will be most urgent during initial heavy rainfall on Thursday. As runoff works its way downstream, the river flooding threat will increase Thursday night into Friday, with numerous area rivers forecast to reach at least minor flood stage.
Marys River flow data predicts that it will reach “minor” flood stage — which is considered to be 20 feet to 21.5 feet — with a crest of 20.24 feet late Thursday night. As of noon Tuesday, U.S. Geological Survey data showed the river level at 6.53 feet.
For flood impacts at 20 feet, the USGS writes, “Expect widespread low land and agricultural flooding. Numerous roads along the Marys are affected and some structures near the river may begin to flood.”
A forecast for Philomath, as of Tuesday afternoon, predicts a 100% chance of precipitation Thursday with a high of 59 degrees. Showers are expected daily from Friday through the following week with temperatures ranging from the mid-40s to low 50s.
“Excessive runoff may result in flooding of rivers, creeks, streams and other low-lying and flood-prone locations,” the National Weather Service said in its flood watch alert. “Flooding may occur in poor drainage and urban areas. Storm drains and ditches may become clogged with debris.”
The alert also warns that landslides and debris flows are possible.
Residents in areas prone to flooding are advised to monitor forecasts and be prepared to take action, if needed.