Keep that rain gear handy and if you live near a river, watch out for more high water. An extraordinarily long current of moisture known as an “atmospheric river” has been aimed at the Northwest, delivering rain, wind and flooding. And there’s more to come.
KPLU weather expert Cliff Mass says it’s not the typical "Pineapple Express" we often see at this time of year.
An Extraordinary Constellation
“Atmospheric rivers are these currents of large amounts of water vapor and they’re generally kind of warm as well,” Mass said, because they usually come from Hawaii and bring tropical air with them.
He says this one is cooler, because it’s coming from a different angle, extending back thousands of miles, all the way towards Japan.
“Because of the configuration of the atmosphere, with a big ridge over the Pacific, it’s causing this moisture to go northward, in the western Pacific, and then angle in towards us,” Mass said, “practically due west to east. It’s amazing,” he said.
He says there isn’t a lot of rain falling out of the river where it’s over the ocean, offshore. But when the currents of moist air approach the coast and are forced to rise by our mountains, the system dumps huge amounts of precipitation. Mass says that’s what’s been happening over the last 24 hours.
“Some places on the Olympics have gotten ten or eleven inches of rain – that’s pretty amazing,” Mass said after checking the rainfall totals Friday morning.
“And a lot of it happened in 12 hours,” He said, noting that the North Cascades saw three or four inches in that time frame as well.
A Wet Weekend Ahead
Mass says the wet weather is by no means over. He expects a break in the rain and stormy weather on Saturday afternoon, after the atmospheric river begins sliding southward Friday night. But he says another push will come in later on Saturday, causing the rain to pick up again.
He says there will probably be a break late on Sunday as well, as we get into cooler and drier air next week.
Flood risks will continue in the Olympics, where the heaviest rain is already falling. But Mass says he’s also worried about western Washington rivers, such as the Skykomish and Snohomish.
“The Cascades are getting hit quite hard; Many of the drainages will have 5-10 inches before this is over.” Mass said.
The National Weather Service is forecasting moderate flooding on several of these rivers and is warning people to take precautions and never to drive over flooded roads, even if they seem shallow.
Snow In The Mountains Should Stay Mostly Intact
Mass says the heavy rain won’t put too much of a damper on the snow that’s been falling on the mountain passes. Skiers hoping to get in some runs before Thanksgiving will likely be in luck.
“We had a lot of snow this week and a number of ski areas have gotten close to enough snow to open. A lot of them have at least a foot, maybe two feet,” Mass said.
He says they might lose 10-15 percent of the snow pack to the rain and it might get a bit icy as some of that rain freezes. But new snow is on the way.
“Probably 10-20 inches in some places, next week,” Mass said. “So I think there’s a really good chance that some of our local ski areas will open.”
He notes that Whistler has already announced it will open November 19.
"And I think there’s a good chance for Baker, maybe even for Stevens and Crystal," Mass said.
The weekly KPLU feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KPLU Environment Reporter Bellamy Pailthorp. Cliff Mass is a University of Washington Professor of Atmospheric Sciences, a renowned Seattle weather prognosticator, and a popular weather blogger. You can also subscribe to a podcast of “Weather with Cliff Mass” shows.
