[Update : Further checking shows that NOAA has not included the last four days of December in the data set, which were very cold. This could alter the outcome]
I just checked over my graph and found a major mistake. Maximum temperatures were warmer in 1934 than 2012, but average temperatures were warmer in 2012 than 1934 and 1921. I had previously mistakenly graphed the maximum temperatures as averages.
The graph below shows the correct average temperatures.