December’s lack of significant snow and cold air masses has been obvious to all Badger citizens, and most would agree that a true Wisconsin winter was not yet established until recently. Two longtime climate indicators of winter have now finally signaled their approval of the season’s start for this year.

Firstly, Lake Mendota’s open waters became closed by ice during the early hours of Saturday, January 14. This date was tied for the fourth latest closing in more than 150 years of records in the State Climatology Office. The first and third latest closings were also in modern times (2002 and 2007). The median dates for the entire record are December 20.

Secondly, the first day that morning temperatures reached down to 0 degrees F this season occurred on this past Wednesday, January 18. In the past 142 years, this ranks the tenth latest for the zero degree mark to be observed. The most extreme delay was in 2002, when the first such day was not experienced until March 3.

In a sense, Lake Mendota behaviors as a kind of thermometer in the late fall and early winter, so there is no surprise of a connection between its delayed closing by ice and the lack very cold air masses. These thermal changes are consistent with the recent trends of warming winters in the northern U.S. as well as of warmer global air temperature.

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Latest revision: 5 March 2012

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