Characteristics Common to Cool Season “Thin Line” Damaging Wind Events
Across the Southern Great Lakes, With a Focus on Northern Indiana
Jon Chamberlain
NWS Northern Indiana
A climatology of cool season (November through March) “thin line” squall lines affecting the Northern Indiana forecast area will be shown. Favorable environments and conditions for the formation and maintenance of a squall line that produces severe damaging winds will be briefly reviewed, highlighting the main differences between warm and cool season events. Research has shown that cool season squall lines/derechos are favored in environments dominated by strong dynamical systems, containing strong wind fields and typically lacking convective available potential energy (CAPE). This pattern has been referred to as the dynamic pattern. The formation and maintenance of dynamic pattern squall lines are similar to their counterpart warm season linear convective system. However, the intense wind fields, strong baroclinic zone, and resultant high shear associated with these systems are solely responsible for the development and maintenance of cool season dynamic pattern squall lines. NSSL/ESRL reanalysis fields of eight dynamic pattern cool season events were created to accentuate the mean synoptic pattern associated with cool season linear convective systems in Northern Indiana. In addition, a small case study of a typical dynamic pattern squall line will be included to further illustrate the synoptic and mesoscale features associated with this type of convective system.