Several storms produced extensive hail damage over Iowa on 9 August 2009. The hail associated with these supercells was observed with radar data, reported by surface observers, and the resulting hail swaths were identified within satellite data. This study includes an initial assessment of cross validation of several radarderived products and surface observations with satellite data for this storm event. Satellite-derived vegetation index data appear to be a useful product for cross validation of surface-based reports and radar-derived products associated with severe hail damage events. Satellite imagery acquired after the storm event indicated that decreased vegetation index values corresponded to locations of surface reported damage. The areal extent of decreased vegetation index values also corresponded to the spatial extent of the storms as characterized by analysis of radar data. While additional analyses are required and encouraged, these initial results suggest that satellite data of vegetated land surfaces are useful for cross validation of surface and radarbased observations of hail swaths and associated severe weather.

Radar data were analyzed for severe thunderstorms that produced severe hail (Ͼ19 mm diameter) across the central and northern plains of the United States during the 2001-04 convective seasons. Results showed a strongly linear relationship between the 50-dBZ echo height and the height of the melting level-so strong that a severe hail warning methodology was successfully deployed at the National Weather Service Warning and Forecast Offices in North Dakota and Iowa. Specifically, for each of 183 severe hailstorms, the 50-dBZ echo height near the hail event time was plotted against the depth of the environmental melting level. Linear regression revealed a coefficient of determination of 0.86, which suggested a strong linear relationship between the 50-dBZ echo height and the melting-level depth for the severe hail producing storms. As the height of the melting level increased, the expected 50-dBZ echo height increased. A severe warning criterion for large hail was based on the 10th percentile from the linear regression, producing a probability of detection of 90% and a false alarm rate of 22%. Additional analysis found that the 50-dBZ echo-height technique performs very well for weakly to moderately sheared thunderstorm environments. However, for strongly sheared, supercell-type environments, signatures such as weak-echo regions and three-body scatter spikes led to more rapid severe thunderstorm detection in many cases.

The complex issue of mesoscale convective system (MCS) dissipation over the central United States is investigated using both observations and Eta Model output from 47 cases that occurred during May-August 1998-99 in Iowa and surrounding states. The cold pool-shear balance theory of Rotunno et al. and Weisman, through tests with observational data, is not found to correlate well with actual dissipation of these MCSs. Differences are discussed that may account for the discrepancies between the results of the present study and the cold pool-shear balance theory. Both surface (SSRI) and elevated (ESRI) system-relative inflow tend to decrease as the MCSs near dissipation, due in part to a decrease in MCS speed of movement. A low-level jet (LLJ) affects most of the MCSs at some time during their life cycles, and there is a tendency for MCSs that were once affected by an LLJ to dissipate once no longer affected by an LLJ. A few cases experience significant decreases in the 850-500-and 700-500-mb lapse rates just prior to dissipation, indicating MCS movement into more stable environments. Maximum 0-2-km equivalent potential temperature decreases during the life cycle, but most often from a very high value to a moderate value that still implies adequate energy for the MCSs. To determine the best model predictors of MCS dissipation, many parameters are examined from the Eta Model. Among these, only a decrease in the 850-mb equivalent potential temperature advection may be a potential predictor of MCS dissipation.

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