Question: The 1947 Glazier–Higgins–Woodward tornadoes were compared to the tornado that took place on what date?
Sentence (from "Tornado outbreak of April 9–11, 2011"): The tornado outbreak of April 9–11, 2011 was one of several tornado outbreaks in the U.S. to take place during the record month of April 2011.
Relevant evidence: No