A radar‐based study of severe hail outbreaks over the contiguous United States for 2000–2011

Abstract

A radar‐based hail climatology, with broad coverage and high resolution, is possible using the Next‐Generation Weather Radar (NEXRAD) Reanalysis through application of the multiradar multisensor (MRMS) algorithm and maximum expected size of hail (MESH). Using 12 years of MESH data, we define a “severe hail outbreak day” and analyse the characteristics and frequency of severe hail and severe hail outbreaks, including an analysis of hail swaths. Thresholds are set to signify severe hail in terms of MESH, and automated quality control measures are implemented. When comparing severe hail days in MESH to reports, we find a linear relationship between MESH and reports. Several case studies are also included to highlight the utility of MESH when studying outbreaks of severe hail, specifically regarding outbreak events that occur in low‐population areas. With the caveat that this is a relatively short‐time period, we find that severe hail days decrease while severe hail outbreak days increase over the period 2000–2011. The increase in outbreaks is happening primarily in the month of June, where the number of severe hail days stays fairly constant over the 12 years. This suggests that the increase in outbreaks is mainly taking place on days when severe hail already occurs. When examining hail swath characteristics, we find that there are a greater number of hail swaths (with a major‐axis‐length [MAL] of at least 15 km) on outbreak versus nonoutbreak days. Additionally, hail swaths with the largest MALs occur on outbreak days.