Wednesday, 5 November 2014
Capitol Ballroom AB (Madison Concourse Hotel)
A multicell cluster of storms moved into northern Indiana during the early afternoon hours of June 29, 2012 and would later evolve into a mature mesoscale convective system (MCS) by the time it reached the eastern portion of the County Warning Area (CWA) of the National Weather Service of Northern Indiana (IWX). This would turn out to be the beginning of a derecho that would continue all the way to the Atlantic coast, traveling 600 miles in 10 hours with an average speed of 60 mph and resulted in 22 fatalities. This derecho produced a measured wind gust of 91 mph at Fort Wayne International Airport, which ended up being the highest measured gust of the entire event. Estimated damages were in the hundreds of millions of dollars and over 4.2 million people were left without power during the heart of a record-breaking summer heat wave. The mesoscale environment was characterized by a quasi-stationary warm frontal boundary, extreme instability (including unseasonably steep mid-level lapse rates,) and weak to moderate vertical shear. Despite a favorable mesoscale environment, the forecast was complicated by antecedent drought conditions. The month prior had featured several rounds of overnight/early morning convection which dissipated quickly before they could reach our area as surface dewpoints frequently mixed into the mid-50s oF by afternoon. So while the potential for severe weather was recognized, extreme drought conditions observed across most of the Midwest during June of 2012 made it difficult to anticipate a high-end event. Adding to the complexity of the event was the ability to maintain situational awareness as forecasters at IWX were challenged to recognize the change in convective mode and the rapid intensification that resulted. This presentation will examine the warning decision making considerations during a high- impact event, including radar interrogation of a rapidly evolving convective mode during the genesis of a derecho as well as the challenges associated with recognizing an anomalous mesoscale environment as a drought biased forecaster.
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