Nathan Hale Library will be closed for renovations May 18-23 and will reopen May 26.
The Storm Prediction Center of the National Weather Service includes maps, tracks, averages and summaries that apply to tornadic activity in the United States. The Norman office of the National Weather Service keeps a historic list of tornado data by county. The EF Scale became operational on February 1, 2007 and is used to assign a tornado a 'rating' based on estimated wind speeds and related damage.
Source: National Weather Service web sites.