The July 2003 Dakota Hailswaths: Creation, Characteristics, and Possible Impacts

Abstract

The authors investigate the meteorology associated with two elongated swaths of crop damage produced by severe hailstorms that crossed North Dakota and South Dakota on 4 July and 20 July 2003. These hailswaths, which were observed in a Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) image time series, each persisted for more than a month and were associated with local temperature increases, presumably owing to the enhanced Bowen ratio over dry, crop-free ground. This paper documents the creation and evolution of the convective storms that produced the hailswaths, and then presents evidence that devegetated hailswaths may impact future convective weather. Idealized numerical simulations including hailswath-like surface anomalies, as well as analogies to the extant literature, suggest that hailswaths may play a part in initiating new convective clouds, especially when the low-level winds are parallel to their long axes. Analyses of conventional operational observations also show that the 4 July hailswath may have played a part in the initiation and intensification of a convective storm on 17 July and in the temporarily deviant motion of a convective storm that crossed it on 20 July. Because devegetated hailswaths are common to the central and northern plains during the summer months, and because they have heretofore received little study, a deeper understanding of hailswaths? impacts upon moist convection may lead to improved short-term weather prediction.