It happens every year. As the summer wanes and fall sets in, people start thinking about the coming winter and how much snow we’ll get, especially in the mountains.
In the Pacific Northwest, that can mean dreams of snowy ski slopes or how much snow pack we’ll have to fill reservoirs and water dry streams when the spring melt comes.
KNKX weather expert Cliff Mass says he has been getting lots of questions on this topic. The trouble is it’s not an easy one to answer with much accuracy.
“Our skill is not as good as we’d like,” Mass says. “We haven’t improved our skill in forecasting weeks to months (ahead) in a long time.”
But there is one set of observations that is the most important tool meteorologists use for predicting the weather months ahead, like the coming winter, for example.
El Niño 101
The tool is called the ENSO or El Niño Southern Oscillation.
It’s a correlation between the temperatures of the water in the tropical pacific and weather patterns around the world, including the Pacific Northwest.
“So in the Pacific Ocean, the temperatures vary substantially,” says Mass, who teaches atmospheric sciences at the University of Washington. “Sometimes they’re warmer than normal in the tropical pacific. And those are El Niño situations. And sometimes they’re cooler than normal. And that’s La Niña.”
The temperatures swing back and forth between these two ends of the spectrum in a cycle that can last 4-7 years. Sometimes, it’s neutral, when the temps settle in the middle.
“You can think of this like a big bathtub. The Pacific is a big bathtub, with the water sloshing back and forth,” Mass says.
A Weak El Niño This Year
Currently, based on these observations “and everything else they have,” Mass says the National Weather Service is forecasting an El Niño for the coming winter months.
“A warmer than normal winter and a little bit drier than normal winter. That’s the official forecast for this entire season, from November to February,” he said.
It’s an El Niño, though it’s looking like it could be a weak one, which makes the prediction game even less reliable. It's possible it could even tip into a neutral situation, which could serve up all kinds of weather.
“And right now, the best models we have are suggesting that this is going to be probably a weak to moderate year,” Mass says. That means the forecast is still pretty unclear.
And even though he calls this “probably the most important tool the weather service is using,” Mass concedes that it’s a lot less accurate than what people who look at daily and weekly forecasts come to expect.
“The problem here is that there is a correlation between the water sloshing back and forth and the weather in our region, but it’s not a perfect one,” he says.
A Dicey Forecasting System
“It explains maybe 30 percent of the variability,” Mass says. “So there’s a lot of uncertainty with the forecast. If you think about the climate and weather being some dice, they’re weighted a bit towards being warmer than normal and less snowpack than normal because it’s an El Niño year.”
But Mass says it’s still quite uncertain. Would he buy a season pass to the ski areas around here?
“I normally don’t, but this is probably a year I might not do that,” he says.
Weather with Cliff Mass airs at 9:02 a.m. Friday, right after BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KNKX 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 podcasts of Weather with Cliff Mass shows, via iTunes or Google Play