The latest edition of the IBHS map representing the frequency of hail reports in the United States reflects the most recent 10 years of hail reports. The map was produced using data from the Severe Weather Database files maintained by the NOAA Storm Prediction Center in Norman, Okla.
The map is based on reports of 1” or larger hail from 2003 through 2012. The techniques for creating the revised map are the same as those used to create the prior frequency analysis for the period from 2000 through 2009. The steps included removing duplicative reports from the dataset, counting the number of reports within 10 x 10 mile grid cells, averaging those counts with neighboring grid cells, and interpolating the transitions in frequency between the 10 x 10 mile cells. A more complete explanation of how the map was created, along with the 2000-2009 frequency analysis, can be found in the IBHS Analysis of Hailstorm Frequency.