NOAA's National Centers for Environmental Information
Snow cover extent began to increase in the northern areas of North America as can be seen in the animated image to the right. Some early season snowfall also occurred in the Canadian and U.S. Rockies. Anchorage, Alaska had its highest September snowfall on record (6 inches), all of which fell in one day (September 25th), also breaking the old record for the heaviest 24-hour snowfall for the month of September in Anchorage.
Although some early snow fell in parts of the western mountains, monthly snow cover extent for the contiguous U.S. was near zero square kilometers as can be seen in the graph to the left. For September, the average snow cover extent is approximately 12,000 square kilometers for the nation, with an additional 184,000 km2 for Alaska. Alaska also had below average snow cover for September with 97,000 km2 less than average.
See NCDC's snow climatology page for snow statistics for U.S.states and stations.