Hundreds of people flocked to City Beach over the weekend to enjoy the rare phenomenon of glassy ice-skating conditions on Whitefish Lake. The depths of the lake could easily be seen through the translucent surface that froze during the recent arctic outbreak, offering a remarkable look at what lies beneath.

The wild ice experience was the buzz around town, and begged the questions: Why is the ice so clear and how often does this happen?

“Clear ice like what we’ve seen on Whitefish Lake this past week contains very few impurities such as air bubbles or plant fragments,” explained Cassie Roberts, a limnologist with Whitefish Lake Institute. “Ice like this is formed when the water is calm and when ice develops slowly over time. Slow ice development means air is less likely to be incorporated into the ice, allowing for the ice to be perfectly clear.”

The lake typically freezes from mid-January to mid-February, depending on conditions like air temperature and wind, Roberts said. Last year, ice was first seen on the lake Jan. 14. This year it started to freeze on Jan. 17.

According to data kept by the institute, the lake completely freezes most winters. However, in recent history, from 1998 to 2023, it has remained partially open about 26% of years.

“Open water winters used to be much less common,” Roberts explained. “Whitefish Lake Institute has data from 1914-1962 that shows the lake remaining partially open water in only 8% of years.”

Because of this change, the institute has been working to collect more data on lake ice in Montana. People can submit information about lake ice when they visit a frozen water body, which will be added to a live ice map on the institute’s website.

“This is a way for us to collect data on when Montana lakes are freezing and provide a map of frozen lakes for people who want to enjoy them,” Roberts said.

The lake observation survey can be found at whitefishlake.org.

Skating conditions at City Beach should remain ideal through Thursday before a potent winter storm hits the region. 

Snow and freezing rain are possible in valley locations Friday into Saturday. By Sunday an arctic intrusion is expected to clash with subtropical moisture, which could produce a major winter storm, the National Weather Service in Missoula warned.