April 2013 was a rather cold month for a good chunk of the Midwest and Plains as seven states were in the top ten for their coldest months of April since the modern climate era began in 1895.
In fact, for North Dakota it was the coldest on record as temperatures on a statewide basis averaged nearly ten degrees below average.
The cold April, brought to you by a strong blocking regime that was a continuation of the blocking pattern that ruled the roost in March, continued to funnel cold air south into the Plains and Midwest for much of the month.
That same pattern was also responsible for the most snow seen in North America in April in nearly thirty years. Much of that increase in snow cover in April was situated over the areas that, not surprisingly, saw the greatest amount of cold last month -- the Upper Midwest and Plains (graphic below from Rutgers). Globally, April's snow cover was the most we've had since the mid 1990's.
The average snow cover extent in the US in the month of April was 480,000 square miles according to the Rutgers Global Snow Lab, which was 209,000 square miles above what's considered "normal" and the 5th largest extent of April snow cover since the 1960's.
More statistical information on April's weather can be found at the NCDC's "State of the Climate" page.