weather map sept 12 2014
Massive early cold wave - Nearly an inch of snow at Rapid City. This is the earliest recorded snowfall going back to 1888.

Mount Rushmore from NWS Rapid City Twitter Feed:
mount rushmore sept 12 2014
A television Meteorologist in Sioux Falls, SD had this to say:
Brandon Spinner ‏@wxSpinner89 Sep 11
Way too early for this. Even the Presidents look like they are crying..."
The national Weather Service in Rapid City posted this on Twitter a few minutes ago, it shows their view outside the window looking at their radiosonde launch station

Rapid City Sept 12 2014
According to a newspaper report from the Sioux Falls Argus Leader, eight inches of snow have reportedly fallen in the Black Hills area. This beats the previous early snowfall record set on Sept. 13, 1970, when 0.7″ of an inch of snow fell at Rapid City, SD.

Elsewhere, 8″ of snow were reported in Downtown Custer, 6″ were reported five miles south of Hill City, and 4-5″ inches were reported in Hill City, Sioux Falls Argus Leader reported. Mount Rushmore reported 7″ of snow, and Sundance, Wyoming reported 4″. The map below shows accumulations.
snowfall USA Sept 2014
Freeze warnings for many northern U.S. locations have also been issued, including Spokane, WA and Duluth, MN.

I expect we will see many many cold records set.