At a Glance

Many locations had severe or extreme winter conditions by late November.December's mild and less-snowy weather pattern contributed to less-severe conditions.

A little over a month ago, the amount of cold and snow in the Plains, Midwest and Northeast ranked near the worst on record for so early in the season, but since then, there has been a drastic change.

On Nov. 27, had already seen an extreme season-to-date of cold and snow, according to the from the Midwest Regional Climate Center.

December's relatively mild temperatures and lack of widespread snowfall has sent that same index into reverse in most areas. As of Jan. 2, only about 10 locations across the Lower 48 remained in the extreme category for the amount cold and and snow recorded to date.

(MORE: Snow Winners and Losers So Far This Winter)

Comparison of the winter misery index from Nov. 27 to Jan. 2.

The index takes into account the "intensity and persistence of cold weather, the frequency and amount of snow and the amount and persistence of snow on the ground," the Midwest Regional Climate Center says. Wind and mixed precipitation, such as freezing rain, are not a part of the index.

For the vast majority of Americans, the index says that winter conditions through early January have been either average, moderate or mild. Those are the bottom three of the five categories – mild, moderate, average, severe and extreme –used to rate the severity of winter weather in cities across the U.S.

Chicago, Detroit and Albany, New York, are some of the cities that have seen a significant turnaround in just over a month.

The flip-flop in those cities and many others is due to how cold and snowy November was compared to average from a persistent southward plunge of the jet stream gripping the central and eastern states. That was followed by a milder and less-snowy December in most locations as the jet-stream pattern changed.

The animation shows temperatures compared to average in November versus December. November was dominated by colder-than-average temperatures in the central and eastern states (blue shadings). December was warmer-than-average in much of the Lower 48 (orange shadings).

(NOAA)

Using the cities mentioned earlier, we can further illustrate the turnaround by comparing snowfall and temperatures from November to December.

Chicago

November: The Windy City had 12.7 inches of snow and an average temperature that was more than 5 degrees below average.December: Just a little more than an inch of snow was recorded, and the average monthly temperature was 5.5 degrees above average.

Detroit

November: Snowfall totaled 6.7 inches, and the average temperature for the month was 4.4 degrees below average.December: The average temperature was 4.4 degrees above average, and less than an inch of snow was recorded.

Albany, New York

November: Just over 10 inches of snow was recorded, and the monthly temperature was 2.7 degrees below average.December: Snowfall was 10.4 inches below average, and the temperature was nearly 4 degrees above average.

The index has worsened for a few cities since late November, including Richmond, Virginia; Raleigh, North Carolina; and Asheville, North Carolina. Much of the blame for that change can be attributed to snowfall from in early December.