What is it about late April?

Boston bombings, an explosion at a Texas fertilizer plant, poisoned letters sent to President Obama and a Mississippi senator, a couple arrested in connection with the murder of a Texas prosecutor - this has been a very strange week, what Washington Post columnist Joel Achenbach describes as perhaps "the most chaotic and unnerving week in recent American history." On that point you might quibble, though what's interesting is that all this terrible stuff is happening in late April, which for some reason has become a time for unpleasantness.

It seems that the third week in April has become our time of calamity. The Branch Davidian fire (1993), Oklahoma City (1995), Columbine (1999), Virginia Tech (2007), the BP oil spill (2010) and now the Boston Marathon bombings all took place between April 15 and 20. For that matter, the Texas City fertilizer explosion of 1947, America's worst industrial accident, happened on April 16. Pattern? The Oklahoma City bombing was timed to be on the anniversary of Waco, but otherwise it's a fluke, a coincidence that the country can hope will fade away amid many peaceful Aprils to come.