The winter of 2007-2008 (Dec. 1st-Feb. 29th) came in as the first "cold" winter since 2000-2001 (11th coldest) after a series of very mild winters between. While this winter will not go down in the record books as extremely cold, it did come in as the 28th coldest for Sioux Falls, which ranks in the top 20% of coldest winters.
As a comparison, the winters of 1978-1979 and 1977-1978 were the 2 coldest winters on record, with average temperatures (taking the high and low each day and dividing by the number of days) of 8.0 degrees and 8.9 degrees respectively. This winter our average temperature was 15.4 degrees.
So, while temperatures have been cold, what has really made this winter seem long is the persistent snow cover. Snowfall has not been excessive, total snow in Sioux Falls for the winter so far is pretty close to normal or a little below normal, but we have been unable to melt what has fallen.
Today (Monday) is the 100th day in a row with at least 2 inches of snow on the ground, which is the 4th longest period of time with this much or more snow on the ground. 100 consecutive days also occurred over the winter of 1971-1972. The longest stretch of time has been 115 days which occurred during the winter of 1968-1969. To reach the 3rd longest stretch, the snowcover will have to last at a 2 inch depth until Friday, which does not appear likely.