Severe wind-driven hail events: dependence on convective morphology and larger-scale environment

Prior studies have examined both the near-storm envionments and convective morphologies most likely to be associated with either severe wind events or hail events, but relatively little work has been done to understand the conditions favorable for severe wind-driven hail events. Some recent cases such as the Eldora Iowa event in August 2009 have demonstrated how tremendously damaging and dangerous a thunderstorm can be when severe wind and large hail occur together. Thus a further examination of these storms that produce these events is warranted.

We will document cases when severe wind-driven hail occurred by comparing the times and locations of severe hail and wind reports in Storm Data, in addition to examining the descriptions of events that are often provided. We will focus on higher-end events using classifications based on SPC's significant severe criteria (hail diameter greater than 2 inches with winds exceeding 65 knots) and Extreme Damaging Wind (XDW) events as defined by Miller and Johns (2000), but will also note more marginal events. We will focus at first on data from 2007 so that we can use the 12 storm morphologies identified in Duda and Gallus (2010) over a 10 state region during April-August of 2007 to determine the specific morphology associated with these events. We will also expand the dataset to include wind-driven hail events from other years, again classifying the morphologies of the storms that produced those events. As in Duda and Gallus, we will use MDA information to classify supercellular storms, and may examine Level 2 data manually as an extra check on the presence of rotation in any storm. In addition, we will analyze several weather parameters often used in severe weather forecasting, including CAPE, shear in several layers, and other stability indices to see how the values occurring with severe wind-driven hail events differ from those present on days when hail alone or severe wind alone are present. Finally, for at least a few case studies, we will examine radar data more closely to determine if bow echo structures were present or if features such as deep convergence zones and Three-body scatter spikes existed.