Cliff Mass: Atmospheric river event will be the strongest storm of 2023

Heavy rain stormed Western Washington over the weekend, courtesy of a recent series of atmospheric river storms, making Monday one of the wettest days of 2023.

And, according to Cliff Mass, a University of Washington (UW) meteorologist, Washington is getting an atmospheric river storm Monday night.

From Ted Buehner: Atmospheric river returns to Western Washington, bringing heavy rains

“The reason that they’re so important is they have strong winds with them and a lot of moisture,” Mass told The Jason Rantz Show on KTTH 770 AM. “When that moisture hits the mountains here, the moisture is forced to rise. That moisture is released as rain, and we can get extraordinarily heavy rain for six to 24 hours.”

This area is home to some of the most atmospheric rivers in the country, occurring most along the Oregon coast and in the Pacific Northwest. Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky, according to the National Oceanic and Atmospheric Administration (NOAA) – that transport most of the water vapor outside of the tropics.

The average atmospheric river carries an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River, with exceptionally strong ones transporting up to 15 times that amount.

“You’re expecting (10 p.m. Monday)-ish for it to really start to hit,” Rantz asked.

“After dinner time, I can’t time it exactly, but roughly dinner time,” Mass answered. “For the next 12 hours, we’ll have this river really directed over us. It’s not only going to be wet, but it’s going to be warm. In fact, it has to be warm, because warm air holds more water vapor than cold air. The freezing level is going to rise to 9,000-10,000 feet so there’s not going to be any snow in the mountains. This is all going to be heavy rain.”

While Mass stated this is far from unusual for Washington residents to experience this time of year, he did claim this is expected to be the strongest rainstorm of the year.

“Certainly the strongest one we’ve had this year so far,” Mass added. “It’s going to be pretty substantial in the mountains. They’re going to get probably four to eight inches, depending on where you are. And here in Seattle, probably about two inches. It’ll be pretty wet.”

The FOX Forecast Center stated, through the combination of three to 12 inches of rain and the melting of the two to four feet of snow on the ground in the Cascade and Olympic mountain ranges, numerous rivers will be in the flood stage, with some major flooding a possibility.

“Some of the rivers will get to flood stage,” Mass said. “Examples include the Snoqualmie River. If you want to have real fun, on Wednesday, go to Snoqualmie Falls. It will be extraordinary … Skagit River probably won’t, but there will be several rivers that will get quite high.”

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Washington is currently working through an El Niño winter, which causes winters to be typically warmer and drier. With an El Niño winter and a destructive fire season, climatologists reported in October that nearly half the state is suffering from either extreme or severe drought, according to The Seattle Times.

“We do need the rain. We’ve been drier than normal for the year,” Mass said. “A lot of our rivers have been dropping to below normal. The snowpack has dropped. The reservoirs are a little bit below normal. So we really need a topping off right now. In these kinds of years, we get less rain than normal, and definitely less snow. So we need as much water as we can get right now, and this is going to be a major refill.”

Listen to the Jason Rantz Show on weekday afternoons from 3-6 p.m. on KTTH 770 AM (HD Radio 97.3 FM HD-Channel 3). Subscribe to the podcast here. Follow Jason on X, formerly known as Twitter, Instagram and Facebook.