Let's look at the Aprils of the past statistically after stretches of cold in mid to late March similar to this one. The coldest stretches between March 15th and 24th were in these years. (So far, this stretch in 2013 (assuming that the extended forecast holds) is ranked 8th coldest.)
How were the temperatures in the following Aprils in these years? Here are the composites for each year. 4 of the 8 occurred before 1910.