The Roaring Fork Valley received a respectable amount of snowfall last week — more than two feet in some places.
But that may not translate to healthy snowpack totals by the end of the season.
Adam McCurdy monitors local climate impacts for the Aspen Center for Environmental Studies.
He said nighttime temperatures aren’t cold enough to prevent the snow from melting during the day.
“Our lower elevations, especially go down to Carbondale, they don't have much snow right now — it all melted,” McCurdy said. “Without those overnight lows, that snowpack is not going to be as resilient to daytime temperatures.”
For much of the globe, climate change has a stronger effect on nighttime temperatures than daytime temperatures.
During the day, Earth absorbs energy from the sun and reflects some of it back into space, but a lot more of that energy is released at night when the sun stops shining.
Greenhouse gases act like a blanket, trapping heat in the lower atmosphere and preventing the planet from cooling overnight. Climate change can also increase cloud cover, amplifying that effect, according to the Union of Concerned Scientists.
Recent research suggests that this trend may be shifting, but at least in the U.S., nights still seem to be warming faster. According to a NASA tracking tool, overnight lows in the Roaring Fork Valley were 8.8 degrees above normal in November and December, while daytime highs were 6.1 degrees above normal.
“Nights are when the snowpack cools off,” McCurdy said. “You can think about it as the snow's defense, and if you don't build up that defense at night, [the snow is] way more susceptible to melting during the day.”
As a result, McCurdy said snowpack is more likely to melt off earlier in the spring, instead of slowly trickling out over the summer, leaving forests drier and more vulnerable to wildfires.
“June, in our watershed, is our driest month. It's also, in Colorado, when a lot of the largest fires have historically happened,” McCurdy said. “In a good snowpack [year], even though we're not getting a lot of rain, it keeps all of our ecosystems well hydrated.”
Snowpack also determines the amount of water available in the Colorado River, and warmer nights make it harder to keep ski trails open when snow isn’t falling.
Many of the nights this season have been too warm for ski resorts to make snow.
A prolonged dry spell at the Snowmass Ski Area forced the company to close its Elk Camp Chairlift for a few days shortly after its grand opening.
“I've lived here since 2008, and I've never seen the skiing company have to close lifts that they've opened for lack of snow,” McCurdy said.
Snowpack levels improved with last week’s storms, but are still well below normal.
There’s still plenty of time for snow to fall, but McCurdy said climate change increases the chances of warm days and warm nights.
