Hmm. My punctuality is 93,4% on time and an average delay of 2 mins. Cancellations are at 1% and this is in March..
The most common reason is "Airport and route traffic restrictions (~ 41.61 %)", whatever that means and second is too short turnaround.
Weather is not a problem for me at Newark anyeay.
I try to use turnaround time with ~1% risk of delay as much as possible, but there are delays anyway.