A Climatology of 1995–2024 United States Warm Season Derecho Events and Analysis of Potential Climate Forcing Associations

Abstract

We identified 147 contiguous United States warm-season (May, June, July, and August) derechos between 1995 and 2024. This results in an average of approximately five derechos each warm season. Using the compiled database, trends in derecho occurrence over the last 30 y were evaluated. The frequency of derecho-producing convection has increased over the past 30 y, most notably during the last 10 y, although the degree to which inconsistencies in storm reporting over the decades and multi-decadal climate variability contribute to this trend is unclear. The number of high-end derechos occurring every year has also increased with time. Spatiotemporal distributions and derecho series are identified, and distributions of severe wind reports across derecho events are presented for the 1995–2024 period. Spatial trends in derecho-path locations emulate the (warm) seasonal shift of mesoscale convective systems and elevated mixed layers across the US, with a poleward shift as the warm season progresses. In addition to the derecho-trend analysis, we also look at associations between annual and monthly derechos with seasonal and sub-seasonal climate-forcing mechanisms. The most notable association is Niño-4 sea-surface temperature anomalies with warming in the central Pacific.