Winter snowpack outlook up in air
The outlook is cloudy when it comes to how much snow might fall in Colorado’s mountains this year.
Questions surrounding when, and the degree to which, a La Niña weather pattern might be forming and affect the western United States have added to the usual difficulties when it comes to making long-range weather forecasts.
“This year, I’ve heard scientists or near-scientists speculate (on) anything from an upcoming whopping winter similar to 1983-84 to ‘look out for drought.’” Colorado state climatologist Nolan Doesken told weather- and water-watchers in a recent email.
“… In the next few months, this will all play out before our eyes. This past year’s ‘El Niño’ collapsed as predicted but did not head into ‘La Niña’ land as previously prognosticated.”
El Niños refer to warm surface temperatures in the eastern Pacific Ocean, and tend to correspond with wetter winters in the southwestern United States, including in southern Colorado.
La Niñas involve cooler eastern equatorial Pacific Ocean surface temperatures, and often result in drier winters in the Southwest and wetter ones in the Pacific Northwest and northern Rockies, including in northern Colorado.
“Right now we’re in kind of a neutral state” between an El Niño and La Niña, said Larry Smith, senior meteorologist with the National Weather Service in Grand Junction.
Neutral conditions aren’t a superb indicator of how winter will shape up, but around Grand Junction they typically lead to kind of a normal water year, but also slightly warmer temperatures that mean the snow line starts at a higher elevation than usual, he said.
A couple of forecasting models show a trend toward a weak La Niña eventually occurring sometime this winter, but the phenomenon can have a time lag in terms of impacts on local weather, which makes predicting its impacts hard, Smith said. He added that the El Niño/La Niña is just one of several factors considered in long-range forecasting.
Colorado’s snowpack fared well last winter during what was a strong El Niño. Meteorologist Cory Gates, who forecasts for aspenweather.net, is bullish about this winter’s prospects for the area around the Aspen ski resort town. He has said conditions are similar to those leading into the epic snow year of 1983-84, according to Aspen media reports.
“I would be very careful in making comparisons with that” year, said Klaus Wolter, a research scientist in Boulder with the National Oceanic and Atmospheric Administration and University of Colorado.
“I’m mildly optimistic” about this winter’s snowpack prospects, he said.
But he said there’s a lot of uncertainty because of the lack of clarity about whether there will be a La Niña or not.
Chris Tomer, a meteorologist for Denver television stations who also specializes in mountain forecasting as a private consultant, said he thinks the winter will end up somewhere between neutral conditions “and La Niña Lite.”
He said he expects Colorado’s northern mountains to benefit from a surplus of snow, with a normal winter in the central mountains and slightly below-average snow for the southern part of the state.
“One thing that’s yet to be seen is how does a la Niña Lite and even just a barely La Niña play out in Colorado,” he said.
Warm ocean temperatures off the Pacific Northwest coast and even off the Atlantic coast also may affect the jet stream that helps determine snowfall in Colorado, he added.