It’s Official – ICE ON for Lake Mendota!

Ice on date beats median freeze date by five days

Despite warm weather in Madison over the weekend, cool nights, light winds, and cold water helped Lake Mendota officially freeze on Saturday, December 15^th. Lake Mendota, the largest lake in the Yahara Watershed, froze eight days after the smallest lake in the watershed, Lake Wingra, which officially froze on December 7^th. Lake Monona officially froze on December 11^th.

The Wisconsin State Climatology Office requires ice to hold for a period of 24 hours before a lake can officially be declared frozen over. After ice took shape this weekend, staff waited to see whether it would hold out through the warm daytime temperatures. The December 15^th freeze date is 12 days ahead of last year’s December 27^th freeze date, and a surprising five days ahead of the December 20^th median freeze date. The latest freeze date for Lake Mendota was January 30^th – which happened in the winter of 1932.

The Wisconsin State Climatology Office makes the official determination as to whether the lake is frozen. The climatologists use the same guidelines they have used for decades to determine whether the lakes are iced over. This allows for a continuity in data collection. Read more: Determining ice cover on Madison’s lakes.