An atmospheric river carrying warm winds and rain brought flood alerts to the Pacific Northwest starting on Dec. 4.
What was otherwise a week of temperatures in the mid-40s and rain was briefly interrupted by an overcast Monday Dec. 4, with temperatures of up to 65 degrees Fahrenheit. This continued into Tuesday Dec. 5, where temperatures reached a high around 65 degrees Fahrenheit.
However, the very next day on Dec. 6, temperatures dropped to 46 degrees Fahrenheit, accompanied by strong rainfall of 0.34 inches, 9 m.p.h. wind, and scattered thunderstorms at night. Dec. 7 saw rainfalls of up to 1.02 inches.
Rainfall for the following week of Dec. 11 appears to be low, as temperatures are beginning to fall into the 30s and 40s again.
This week, there has been little to no precipitation and temperatures have ranged between 38 and 50 degrees.
According to UO geography professor Daniel Gavin, atmospheric rivers are a common phenomena that account for around half of the Pacific Northwest’s annual rainfall.
“The link to anthropogenic climate change is always difficult to say,” Gavin said. “But the event fits within the trend that’s been occurring, which is consistent with human-caused climate change. You have warming ocean temperatures in the western Pacific, which is the source region for the river’s moisture, and there’s a well-documented warming trend that has been happening there.”
While El Niño has been occurring this year as well, there isn’t a very strong link between the atmospheric river and El Niño, Gavin says.
“There’s a stronger link with something called the Pacific Decadal Oscillation, or the PDO. That makes sense, because the PDO is a measure of the ocean temperatures of the Pacific Ocean. And there is a very strong link between warm ocean temperatures and a lot of atmospheric river rainfall,” Gavin said.
The atmospheric river has prompted flood warnings in Northwestern Oregon, including Lane County.
According to UO spokesperson Angela Seydel, there isn’t much potential for flooding on campus, however standing water is “likely to occur.”
Safety and Risk Services staff and Campus Planning and Facilities Management staff are always on duty, ready to activate an emergency response in event of a flood.
In Portland, flooding from the atmospheric river has resulted in at least two deaths. While other years have seen worse atmospheric rivers, namely 1996, this atmospheric river is expected to be the worst one of the year.