Find out by going to Climate Central’s post, See How Much Winters Have Been Warming in Your City. The winner is Burlington, Vermont, with about 7 degrees F of warming since 1970 (graph here from the post). There is a drop down menu where you can select from most major cities in the U.S. They don’t provide the data, unfortunately, but they do provide a clear methodology so that you can create the data set for your city. You can get weather data from NOAA Climate Data Online. There is great potential here for student projects in statistics courses.