NWC REU 2005
May 30 - August 6



Hail Warning Decision Guidance

Michelle Harrold, James LaDue, Paul Schlatter, and Gregory Stumpf



National Weather Service (NWS) forecasters will have several new hail diagnostic attributes available to them in Advanced Weather Information Processing System (AWIPS), beginning with the Operation Build version 6 (OB6). In a warning decision environment, it is essential that forecasters have the best guidance available to them. Therefore, the purpose of this study is to determine compare these new hail diagnostic attributes with legacy attributes to determine which attributes are “best predictors” for hail warning guidance. This study is the first step in developing official NWS Hail Warning Guidance training information for warning forecasters.


A total of 11 hail producing storm events were analyzed. The events chosen had geographic diversity across the United States, and included events from both the warm and cool seasons. For each individual hail report, the values of 17 different hail diagnostic parameters were recorded. Each attribute was compared to ground truth reports, and the statistically analyzed, including the calculation of various correlation coefficients, as well as analyses of probability of detection (POD), false alarm rate (FAR), critical success index (CSI), and the Heike skill score (HSS) for varying forecast decision thresholds, as well as different severe hail criteria (i.e., not just 2 cm diameter). Results indicated that the new high-resolution hail diagnostic attributes outperformed the legacy hail diagnostic parameters. Suggestions for future work to complete the development of NWS Hail Warning Guidance are offered.

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