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Thaw Thoughts

Everything you ever wanted to know about Spring on Lake Mendota.

John Allen
March 23, 2015

Spring officially arrived on March 20, and signs of the season are all around Madison: the days are lengthening, the snow is melting, high-schoolers are swarming the Kohl Center for state tournaments, and as soon as the mercury hit 50, UW students put on their shorts.

But winter’s grip remains tight on Lake Mendota, where the only breaks in the arctic scenery are ice-fishing and makeshift hockey rinks. When will the lake melt?

Soon, says the UW’s Department of Atmospheric and Oceanic Science — if this is an average year, the lake will open on April 4.

The department has kept tabs on the lake, and with assistance from the State Climatology Office maintains records dating back to the winter of 1852–53. April 4 is the median date that Lake Mendota loses its ice cover. Those records show that the median date that the lake freezes is Dec. 29, and it’s median length of ice cover is 105 days.

This winter was a little milder than average — the lake didn’t freeze over until Jan. 2, 2015.

The trend over the last century and a half shows a slow, uneven shortening of Lake Mendota’s ice cover. In the 1850s, the lake was frozen over for about 119 days. In the 2010s, that average is about 90 days.

For those who are curious, the longest lake freeze was in the winter of 1880-81, when Mendota was covered with ice from Nov. 23 until May 3, or 161 days. The shortest Mendota winter was 2001–02, when ice cover lasted just three weeks total: Jan. 2–12, and then again from March 4 to 15.

As of Monday, March 23, Mendota has had ice for 81 days.

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