A sprawling spring storm is bringing multiple hazards to the West, Great Plains, and Midwest on Tuesday, before moving east and setting off more severe thunderstorms in the Mississippi River Valley later in the week. The storm is delivering a crushing load of heavy snow to parts of the drought-plagued Plains, with the greatest amounts falling in South Dakota, where the National Weather Service is forecasting upwards of 2 feet by the time the snow winds down on Wednesday.
Blizzard warnings were in effect for parts of Colorado on Tuesday due to the combination of heavy snow, frigid temperatures, and strong winds that were lowering visibilities down to a quarter mile or less at times. The storm came as quite a shock for Denver residents, as Monday’s high temperature was a balmy 72°F. On Tuesday morning, the thermometer dipped to near record cold territory, with an air temperature of just 15°F.
On Monday evening, tornado warnings were issued in eastern Colorado while winter storm warnings and advisories were also in effect, which is a rare occurrence that demonstrated the rapidly changing weather conditions at the time.
Moderate to heavy snow is expected to fall on Tuesday from the Central Rockies to the Central Plains, with snow also breaking out in the Upper Midwest. A heavy, messy wintry mix of snow, sleet, and freezing rain is likely from northeastern Nebraska into southern Wisconsin through Wednesday morning.
Spring snowstorms are not uncommon in Colorado, Wyoming, and Nebraska, but this storm is noteworthy for dumping such heavy amounts of snow and for the extremely cold temperatures that it is helping to bring southward out of Canada.

http://www.huffingtonpost.com/2013/04/09/south-dakota-blizzard-midwest_n_3045841.html