The month of April is typically 10.5 degrees milder than the month of March. April 2020, however, was just 2.4 degrees milder, making its average temper the third closest to March of any April (going back to 1869). The closest April came to March was in 1946 when April was 0.8 degrees milder than March. The chart below lists the six Aprils that were closest to March's average temperature.
And although April 2020 wasn't chillier than March, it had no days in the 70s while March had three (making this the first April since 1940 not to have any readings of 70° or warmer).