This is a really keen project! And I do like your image of NYC slowly sailing southward. (Imagine the wake!)

I think decade by decade is likely to be better than lumping together bigger gobs of data. (Are you using Calc or Excel or what? Wonder if the NWS has a database that is set up for easy data-grabbing.) And looking at winter lows and highs might be good, too. And looking at annual temperature extremes. And analyzing all the weather data that ever were! ... Or maybe not.

But yes, fascinating. Thank you.