Updated: When Will Our Lakes Freeze? Time for Annual CFL “Ice On” Pool

Statue of Liberty replica on frozen Lake Mendota © UW-Madison News Photo by:  Jeff Miller, 1996
Statue of Liberty replica on frozen Lake Mendota
© UW-Madison News
Photo by: Jeff Miller, 1996

Note, post was originally published 11/28/16 and has been updated to include current conditions.
 After a rather balmy Thanksgiving, where nighttime lows still hovered above freezing, our forecast calls for highs in the 30s (Fahrenheit) and lows in the 20s this week, which means it’s the time of year when we try to do the impossible at the CFL – predict when Lake Mendota will freeze. The CFL “ice-on pool” is, essentially, our limnological version of college basketball’s “March Madness.” (The winner must use their proceeds to bring in awesome treats for the lab, so we are all invested in the outcome!)
Last year, December 27th was the date that ice covered Lake Mendota from Picnic Point to Maple Bluff. So what’s in store this year and how will it compare to previous seasons?  While we wait, here are some thoughts on what we’ve seen from previous “ice-on” seasons.
John Rodstrom's amazing Rice Krispie treat concoction at the CFL staff meeting.
John Rodstrom’s amazing Rice Krispie treat concoction at the 2016 CFL staff meeting.

First, let’s all admit that we humans are terrible about remembering weather. I took the dog on a walk this rather warm weekend and found the sight of fishermen out on their boats jarring. “It’s so weird to see people out on the water,” I thought.
Except I was wrong.
It’s not all that unusual and, in fact, it’s probably something I say almost every year (for reference, here’s a 2012 blog post!).
Lake Mendota, January 2012. Still waiting on ice cover. Photo; A. Hinterthuer
Lake Mendota, January 2012. Still waiting on ice cover. Photo; A. Hinterthuer

With our currently weather, anyone submitting a date earlier than December 20th (which is Mendota’s median “ice on” date) is likely to be an overly optimistic ice angler. But it’s difficult to pin November temperatures on freeze dates for our lakes. For example (and a big thank you to the state climatology office) in 2013, Lake Mendota froze on December 16th, well before the median date and, indeed, remarkably cold temperatures in November preceded that freeze (remember the “Polar Vortex?”). While the very next year saw another cold November, a sudden spike in early December temps kept the ice away until January 2nd.
Here’s a list of recent freeze dates, linked to corresponding blog posts when available:
Lake Mendota, winter 2013. Photo: Adam Hinterthuer
Lake Mendota, December 2013. Photo: Adam Hinterthuer

2017 – December 27th. 
2016 – January 1st. 
2015 – January 11th.
2014 – January 2nd.
2013 – December 16.
2012 – January 14.
2011 – January 14.
As you can see, during this decade at the CFL a December freeze has been, well, rare. Of course seven years barely tells us anything about the “ice-on” trends of Lake Mendota. Thankfully, we have the Wisconsin State Climatology Office and they have records dating all the way back to 1852.
 
Historic "Ice On" Dates for Lake Mendota Credit: Aaron Stephenson
Historic “Ice On” Dates for Lake Mendota Credit: Aaron Stephenson

This 150+ year-old record shows freeze dates getting later and thaw dates getting earlier as a January ice on becomes much less unusual. However, the latest freeze date ever recorded (January 30th) was in 1932 – so, while long-term ice data can show that our average freeze date is getting later and later in the year, it is not a great tool for trying to predict what will happen in a single solitary year.
That’s the difference between weather and climate, really – you only see the trends when you can look back over many, many years. Trying to call it in the midst of the current year’s single data point is, well, a little foolhardy. Which is why the CFL’s Ice On Pool will continue to be both a whole lot of fun and anyone’s guess.
As far as my unprofessional opinion goes, there’s no way Mendota freezes before Christmas. Or, well, I could be wrong!
 
 

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