If you don't take this week's Nor'easter into consideration, we've actually experienced some above average temperatures lately. Often a warm spell in the middle of fall, after the first frost, is referred to as "Indian Summer." The National Weather Service defines Indian Summer as "an unseasonably warm period near the middle of autumn, usually following a substantial period of cool weather." Take last weekend for example: Saturday reached 60, Sunday was a balmy 74, Monday we got to 71, and Tuesday's high was 66. The normal high for this time of year is 58 degrees.
The typical weather pattern promoting Indian Summer is high pressure right along or just off the east coast. That allows warmer air to flow in from the south. In the fall it is typical for several fast moving low pressure systems to dive into the region, bringing an end to the warm spell, but the pattern often repeats itself until eventually the cold air mass wins out as we enter winter.