Several atmospheric rivers set to drench Western WA this week and next

It’s been relatively dry in Seattle and western Washington for the first half of this week, but dry periods are about to become few and far between, with several atmospheric rivers on their way to drench the region.

Seattle meteorlogist Scott Sistek told “Seattle’s Morning News that lighter atmospheric rivers are helpful and beneficial to the region, while others become too strong and can cause several issues, including flooding.

“The ones for this week, we kind of start on the beneficial side. They’re not too bad. It’ll be wet and kind of warm, but not like super rainy,” Sistek said. “And then as we get later into the week, this weekend into next week, that’s when we’re looking at some stronger storms. Combined with the earlier storms, you put them all together, and now we’re putting some pressure on our rivers.”

Chances of floods won’t occur this week, but could pop up as soon as next week.

“Middle to late next week, we’ll start having to really keep an eye on our area rivers because, by then, we will have had two or three of these storms move through here,” Sistek said.

What is an atmospheric river?

The term “atmospheric river” first appeared in modern scientific literature in the early 1990s, sparking debate among atmospheric scientists and climatologists about its exact meaning.

“It’s kind of become a favorite term in the media here and amongst meteorologists. It basically describes a weather pattern where you get a long fetch of moisture that has tapped into the tropics,” Sistek said.” So in our case, it taps into moisture around the Pacific Ocean, right around the tropics, where that moisture is warm, and there’s quite a bit of it, and then it’s like a conveyor belt. It shifts it from down in the tropics, pulls it up across the ocean, and then kind of aims it right at the Pacific Northwest. So, we call it an atmospheric river because it looks like a river on the map.

“It is almost literally like a river of moisture that goes from the tropics straight up into our area,” Sistek added.

Atmospheric rivers can contain as much water as 25 times the entire volume of the Mississippi River.

“So that is a lot of moisture in the atmosphere, and it’s why, when we get the really big atmospheric rivers, we have a lot of concern,” Sistek said. “That means there’s going to be a lot of rainfall and, since it’s tropical moisture, it’s not cold rain either. It’s warm rain, so that usually pushes up the snow levels.”

Snow levels

Due to several atmospheric rivers bringing warmer rain into the region, it’s made the region wetter and warmer, leaving skiers to ask, “Where’s our snow?”

“We’ve been talking about La Niña for a few months here, and usually La Niña winters tend to be a pretty good snow producer in the mountains,” Sistek said. “This winter so far, nothing is up there. There’s only, like, a few inches at best. So, skiers, not a lot of good news, at least through the middle of December.”

Are we going to have a white Christmas?

With just three weeks until Christmas, those living in western Washington are wondering if this will be the year a “white Christmas” happens. There is a 7% chance of a white Christmas in any given year, as it usually occurs every 13 years.

“I think the last one was 2007. I should have looked this up, but we’re probably due, and I feel like LA Niña is going to come to us at some point. I think, at some point, the ridge that’s been keeping us warm, if that moves over, then we get the cold air that’s been going east. Maybe mid- to late-December, we can start getting into the cold air fun, and maybe we can time something up for Christmas.”

Charlie Harger is the host of “Seattle’s Morning News” on KIRO Newsradio. You can read more of his stories and commentaries here. Follow Charlie on X and email him here.