Examination of the Forecast Process, Mesoscale Environment, and Evolution of the Northern Indiana/Northwest Ohio Derecho of 29 June 2012

Abstract

A multicell cluster of thunderstorms moved into northern Indiana during the early afternoon hours of 29 June 2012, later evolving into a mature bowing mesoscale convective system (MCS) by the time it exited the County Warning Area of the Northern Indiana National Weather Service. This was the beginning of a derecho that would continue across the Appalachian Mountains and off the Atlantic coast, traveling 1000 km in 10 h and resulting in at least 18 fatalities. This derecho produced a measured wind gust of 41 m s-1 (79 kt) at Fort Wayne International Airport, the highest measured gust along the derecho’s path. The mesoscale environment was characterized by a strong cold pool, extreme instability (including near-record steep midlevel lapse rates), and weak to moderate vertical shear. This paper examines the source of this extreme environment as well as the catalyst for the sustainability of the MCS.