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Where can I find information about tornadoes that have occurred in Tulsa and in Oklahoma?

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.