Temperature fluctuations in the winter have no effect on the water temperature under the ice except for the top few feet. Once ice cover is established water temperatures stabilize around 4 degrees Celsius throughout the water column. Different storey during the open water season.
I believe without a doubt though, that the pressure changes associated with those warm/cold fronts impact fish behaviour. During the open water you just have the additional variable of water temp on fish behaviour.
Fish stable weather, approaching low pressure, rising pressure after a period of low and any other time you can get away from work and home!!!
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Bruce Ogilvie
"Fish Hard, Hunt Hard, Live Hard"
http://www.muskiescanada.ca/