Quantification of Mechanisms for Damaging Wind Generation in the 29 June 2023 Derecho Event using the Weather Research and Forecasting (WRF) Model

A cluster of overnight storms in the Central Plains grew into an intense mesoscale convective system (MCS) as the cluster translated into the Midwest during the morning and early afternoon hours of 29 June 2023. The MCS produced widespread damaging winds, including a swath of estimated 100+ mph gusts in western Illinois, hundreds of preliminary storm reports, a handful of tornadoes, and is considered a potential billion-dollar disaster. Owing to the widespread nature of the long-lasting MCS’s damaging winds, the MCS likely meets derecho criteria.

Damaging winds in MCSs are known to be produced by different mechanisms including downbursts (DBs), rear-inflow jets (RIJs), and mesovortices (MVs). DBs are strong, typically precipitation-driven downdrafts that can extend to the surface and then spread horizontally outward. An RIJ is an internally driven horizontal jet of tens-of-kilometer width which typically resides a few kilometers above ground level and then descends to the ground. Finally, MVs are vertical vortices with several-kilometer diameters which form at or just behind the leading-edge gust front. These mechanisms can act alone or in tandem.

The 29 June 2023 derecho event was simulated with the Weather Research and Forecasting (WRF) model to investigate the wind-generating mechanisms in the long-lasting, intense MCS. High-resolution output was used to objectively identify severe and potentially damaging winds and associated generating mechanisms. Model output was compared to wind reports to evaluate the veracity of the simulation and attribute modeled mechanisms to observed reports.

Model analyses indicate that the RIJ was the most frequent generator of modeled severe and potentially damaging winds in the 29 June 2023 event simulation. DBs generated significantly less severe and potentially damaging winds, although the winds, on average, were of similar intensity to those generated by RIJ. MVs generated severe and potentially damaging winds slightly more frequently than DBs and were the strongest solo mechanism, with the highest mean wind speed and percentage of winds that met or exceeded significant severe criterion (33.4 m s^-1). These results will be compared to three separate billion-dollar disaster derecho events, representing different meteorological environments, geographic locations, and seasons, to test the generality of the findings.

With a better understanding of RIJs, MVs, and DBs, and their ability to generate damaging winds, these mechanisms could be incorporated into wind engineering models, allowing for improved risk assessment and ultimately contributing to the design more resilient structures in the future. Such understanding could also be used to enhance operational warnings of severe winds.