I call the Winnipesaukee Data Phone. They report several data points including the Lake Temperature. I post that from time to time at
www.rattlesnakecam.com/watch.htm.
I use this because it is what has been used for many years. Yesterday and todays temp was 37. The previous two days were 35, then 36. My recollection is that ice out happens at 39 or warmer.
603-527-0071 The lake temp is the last data point he reads right after the precipitaition.
IG