The Giants dominate October while the Panthers shine in December. In Green Bay, the Pack has winning records in September, October, December, and January, but drop to 50% in November. The Raiders and Broncos steadily decline throughout the season. It could be weather, or playoff situation, or injury issues but the month of the year seems to have a considerable effect on some teams success.
Of course, there are teams that are immune like the Patriots and Browns, obviously for different reasons.
We compiled all NFL records since 2002 by month to create the graph below. You can view the results as either totals or percents. Use the drop down to change teams.