November 2011 had its ups and downs, but it was a mild month overall at 4.4 degrees above average. The reason we were mild is that the jet stream mainly lined-up from west to east across the northern tier states, or from southwest to northeast from New Mexico into the Great Lakes(typical of a La Nina pattern).
Things could change as we head into December. Although the first few days will be near or slightly above average, colder air will start invading the Midwest as soon as next week. This is partially because the North Atlantic Oscillation (NAO) is expected to go from positive to near-neutral, or even negative later in the month. A more negative NAO tends to send the polar jet stream further south on the North American continent.