Analysis of TORRO’s database for 1930–2009 identified 620 hailstorms that reached a significant, damaging intensity of H2 or more.
The early summer experiences the highest proportion of such storms, with 50% occurring in June (27%) and July (23%). A separate analysis of hailstorms of intensity H5 or more (specifically H4–H5 or more and usually involving hail ≥50mm diameter) which have occurred in Great Britain from 1800 to 2009 indicated that the peak monthly incidence of these more severe storms is slightly later than for all hailstorms of intensity H2 or more, with July accounting for 41% of these events followed by June (21%); 93% occurred between May and August (Webb and Elsom, 2016).
The full database of H5+ storms can be accessed in Appendix A
of Extreme Weather: Forty years of the Tornado and Storm Research Organisation
The area most frequently affected by hail damage extends from Lancashire, Greater Manchester, and Merseyside, southeastwards to the counties in and around the Thames Valley (Berkshire, Bedfordshire, Buckinghamshire, Hertfordshire, Oxfordshire) and Greater London, and to parts of East Anglia (Cambridgeshire, Essex and Suffolk). The geographical distribution of storms of H5 intensity or more indicates a conspicuous maximum occurrence towards the south-east Midlands and central East Anglia (Webb and Elsom, 2009 and 2016).
Webb, J.D.C., Elsom, D.M., Meaden, G.T. (2009) Severe hailstorms in Britain and Ireland, a climatological survey and hazard assessment. Atmospheric Research, 93, 587–616.
Webb, J.D.C., Elsom, D.M. Severe hailstorms in the United Kingdom and Ireland: a climatological survey with recent and historical case studies. In: Extreme Weather. Forty years of the Tornado and Storm Research Organisation (TORRO), 1st Edition. Wiley-Blackwell and John Wiley and Sons: Chichester, UK (Chapter 9).