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Ensemble Forecast Products for the 14 April 2012 Severe Weather Event in Nebraska

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Wednesday, 7 November 2012
Symphony III and Foyer (Loews Vanderbilt Hotel)
James R. McCormick, UCAR, Offutt AFB, NE; and E. Kuchera and S. Rentschler
Manuscript (1019.1 kB)

During the 21 hour period between 15Z 14 April 2012 and 12Z 15 April 2012, widespread severe weather occurred over southern and central Nebraska. All modes of severe weather were noted, including tornadoes, baseball sized hail, and 80 MPH winds. The severe weather, in various forms, occurred over the course of the entire 21 hour period, including several rounds of severe weather. The mode of severe weather included both supercellular and linear storm structures.

The event was well forecast; Storm Prediction Center and National Weather Service forecasts all indicated a strong likelihood of severe weather in Nebraska. These forecasts included a “high risk” designation for much of eastern and central Nebraska. Details of the forecast, however, remained challenging, specifically the timing of convection initiation, the mode of convection and behavior of storm propagation, and the locations facing the greatest severe weather threats.

At the Air Force Weather Agency, several severe weather forecast products are routinely developed using the Mesoscale Ensemble Prediction System (MEPS). These products include various probabilistic products, including for thunderstorms, supercells, tornadoes, hail, and damaging wind gusts. Deterministic products, such as simulated radar reflectivity, are also available. These forecast products painted a convoluted picture on 14 April involving early convection, clustered storm modes while maintaining a significant severe weather risk in southeastern Nebraska. The goal of this presentation is to discuss the various modes of severe weather that occurred over southern and central Nebraska, as well as discuss the performance of AWFA MEPS and its value to forecasters in their attempts to specify storm type and storm timing.