March snow is not unusual in northern Illinois and northwest Indiana. In Chicago, the normal March snowfall is 5.6 inches and the seasonal normal is 36.7 inches. So about 15 percent of Chicago's snow falls in March. For Rockford, the normal March snowfall is 4.8 inches, or 13 percent of the annual normal of 36.7 inches.
In Chicago there have been 45 snow storms that produced at least 10 inches of snow, since snowfall records began in 1886. Six of them, or 13 percent, were in March. The largest March snowstorm in Chicago history was 19.2 inches on March 25 and 26, 1930. It was the 5th biggest snowstorm in Chicago history.
As of midnight March 5, 2013 there was 9.2 inches at O'Hare Airport. This is the biggest March snow in Chicago in a calendar day since 11.5 inches fell on March 2, 1954. This is the most snow in the month of March since 11.2 inches fell in March 2002.
As of midnight AM March 5 there was 9.6 inches in Rockford. This is the biggest March snow in Rockford on a calendar day since 10.4 inches fell March 29, 1972. This is the snowiest March since 10.4 inches fell in March 1999.