Deep freeze has yet to hit Madison lakes

Wide swaths of lawn aren’t the only odd sight on campus this late in December.

There is still all kinds of open water on either side of Madison’s isthmus, as ice has yet to take hold on lakes Mendota or Monona.

That didn’t get odd in an official way until the last week, when the still-liquid lakes passed their average freeze-over dates. Lake Mendota is completely covered by ice by Dec. 20, on average, according to the Wisconsin State Climatology Office, affiliated with the Department of Atmospheric and Oceanic Sciences. Smaller Lake Monona is usually covered, on average, by Dec. 15.

“It’s Wisconsin,” says Stephen Carpenter, director of the UW–Madison Center for Limnology. “So expect the unexpected.”

That’s cold comfort to entrants in the Clean Lakes Alliance-sponsored Mendota Freeze Contest, who are vying for cross country skiing gear by picking the day the big lake is completely iced over.

That’s not to say that Carpenter, who spends an awful lot of time around lakes, can’t provide some insight. Turns out, it’s not that unusual for some portion of Lake Mendota to be open in late December.

“It’s not unheard of,” Carpenter says. “Since 1856, there have been 24 years when the lake froze (first) in January. However, late freezes are becoming more common.”

Mendota’s average freeze date for the first 125 years of data — from 1856 to 1980 — was Dec. 18. But warm weather in the last few decades has tipped the calendar by more than a week.

“Since 1980, the average freeze date has been Dec. 27,” Carpenter says. “Since 1990, the lake has frozen in January in seven years, which is 29 percent of all the late freezes in only 20 years.”

Of course, the latest freeze-over date comes from all the way back in the winter of 1931-32, when Lake Mendota was sloshing around until Jan. 30. The earliest freeze was in 1880, on Nov. 23.

But will we still see open water as the spring semester kicks off?

“It’s all about the weather,” Carpenter says.

There’s not much meaningful change expected on that front. The forecast calls for high temperatures in the mid- to upper-30s, and even lower 40s by the weekend. Low temps will range generally in the upper 20s.

Of course, it may not even be March before we’re thinking about thaw dates. Warm-blooded folks, take note: the earliest Lake Mendota’s ice has ever opened was in 1998 on Feb. 27, less than 70 days away.