Map Information:The map is titled, “Tornado Activity by County: 1996-2013.” It depicts a map of the continental United States, Puerto Rico, Alaska, and Hawaii including state boundaries. It includes data from the NCDC Storm Events Database. All tornadoes classified as F0-F5 or EF0-EF5 are included. F-scale and EF-scale tornadoes are grouped as equivalent for consideration of frequency categories.Map description: The frequency of tornadoes from 1996 to 2013 is represented by four categories.The first category includes counties that have recorded the highest frequency of F3 or EF3 or stronger tornadoes or from four to seven (4-7) tornadoes at the F3 or EF3 or greater level. The areas of the United Stated in this category include from one to several counties in Nebraska, Kansas, Oklahoma, Arkansas, Tennessee, Mississippi, and Alabama.The second category includes counties that have recorded the second highest frequency of F3/EF3 or stronger tornadoes or from one to three (1-3) tornadoes at the F3 or EF3 or greater level. The areas of the United States in this category include one or more counties in Arizona, Montana, North Dakota, South Dakota, Nebraska, Colorado, Kansas, Oklahoma, Texas, Louisiana, Arkansas, Missouri, Iowa, Minnesota, Wisconsin, Illinois, Kentucky, Tennessee, Mississippi, Alabama, Indiana, Michigan, Ohio, New York, Pennsylvania, Maryland, Virginia, North Carolina, South Carolina, Georgia, and Florida. The area with coverage by this category goes from north to south from North Dakota and Minnesota on the north to Texas, Louisiana, Mississippi, and Alabama on the south including the states in between. There is a second area of this category that goes from west to east from Kansas and Oklahoma on the west side, through Arkansas, Tennessee and Mississippi to Alabama and Georgia on the east.The third category includes counties where the largest recorded tornado has been at the F2 level or below (levels EF2, EF 1 or EF0). The states with counties in this category include most or all of every state not previously listed in the states with higher level tornadoes and Puerto Rico.The fourth and last category includes counties with no recorded tornadoes. States with counties in this category include most of Alaska, West Virginia, and Puerto Rico, areas of several counties in Washington state, Oregon, California, Idaho, Utah, Nevada, Arizona, Montana, Wyoming, Colorado, New Mexico, Nebraska, Texas, and Vermont, and small areas of South Dakota, Nebraska, Minnesota, Missouri, Wisconsin, Michigan, Indiana, Ohio, Kentucky, Tennessee, Louisiana, Maine, Massachusetts, New York, Pennsylvania, New Jersey, Virginia, North Carolina, Georgia, and Florida. Overall, most of the US is included in one of the first three categories that have had some level of recorded tornado.Federal Emergency Management AgencyORR Mapping and Analysis Center, Washington, D.C., March 13, 2014. Sources: ESRI, USGS.
