Why isn’t Dillon Reservoir frozen over yet? | SummitDaily.com

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Why isn’t Dillon Reservoir frozen over yet?

Summit Daily/Mark Fox

Ski lifts are running, snow tires are in fashion and hills and towns are buried under more snow than has been seen in recent Decembers. All around Summit County, the winter season is in full swing. Everywhere, that is, except Dillon Reservoir, which remains stubbornly un-frozen even as the new year approaches.

Experts say the reservoir, which at press time had a thin layer of ice around the sides while the core remained liquid, is only a few days behind schedule and is likely to freeze soon as temperatures are forecast to drop well below zero.

“With the cold temperatures they’re predicting for the next couple of days I imagine it’ll freeze over,” Dillon Marina manager Bob Evans said Thursday. “What you need is cold nights without much wind, that’s what makes the thing freeze.”

If the reservoir finally ices over tonight, it will be the latest freeze in 10 years.

Of course, it would still be far from the longest the ice has held out. The latest freeze on record was in 1981, when the reservoir didn’t ice over until Jan. 31. The earliest freeze the reservoir has ever seen is early December, according to data from Denver Water. Generally the water has a full layer of ice by sometime during the week between Christmas and New Year’s.

It is unclear, based on annual data, what climate factors cause the freeze date to swing so dramatically. Neither yearly high temperatures or water levels appear to impact the freeze date. The warmest temperature in 1981, the latest freeze on record, was 81 degrees, only a few degrees below the year of the earliest freeze, according to Evans.

The latest freeze in recorded history also fell during a drought period, when lower water levels did nothing to induce an earlier freeze date.

Whatever the cause, the freezing of Dillon Reservoir is a topic of interest in the community for reasons both logical and otherwise.

While ice boaters are always eager to get their sport’s very short season under way, Evans said he also fields plenty of calls from people, inexplicably concerned that the water freezing will impact snowfall at Keystone.

A popular mountain myth suggests that Dillon and Keystone get less snow if the reservoir is not frozen. In reality, the reservoir’s freeze date is unrelated to snowfall, Evans said.

“There’s an awful lot of misconceptions with the weather up here,” he said. “If you look at the snowfall amounts and when we get it, that has nothing to do with it.”

The date of the lake’s freezing has no real impacts on the surrounding environment or wildlife.

The reservoir is usually completely free of ice by May.