The Initiation and Evolution of Multiple Modes of Convection Within a Meso-Alpha Scale Region
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Date
2007-10-25
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Abstract
On 30 March 2006 a convective episode occurred featuring isolated supercells, a mesoscale convective system (MCS) with parallel stratiform (PS) precipitation, and an MCS with leading stratiform (LS) precipitation. These three distinct convective modes occurred simulataneously across the same region in eastern Kansas. Multi-modal events are especially challenging for forecasters given the wide range of severe weather threats that accompany the different modes. In order to better understand the mechanisms that govern such events, this study examined the 30 March 2006 episode through a combination of an observation-based case study and numerical simulations. From the results of this study we conclude that, for this event, localized environmental variations were largely responsible for the eventual convective mode, with the method of storm initiation having only limited effects. The resultant mode was very sensitive to both the environmental thermodynamic and shear profiles, as variations in either led to different convective modes within the numerical simulations. Finally, we conclude that while the individual modes each developed within an environment distinctly favorable for that mode, they were able to persist in close proximity to one another due to a "middle ground" environment permissive of all three. Strong vertical shear and moderate instability led to the development of supercells in western Oklahoma and similarly strong shear oriented parallel to a surface dryline coupled with dry air in the middle and upper levels led to the development of the PS linear MCS in central Kansas. Meanwhile, moderate wind shear coupled with high instability and strong linear forcing led to the development of the LS MCS in eastern Kansas. Without this linear forcing, the moderate shear environment was supportive of both linear and isolated supercell modes, resulting in the storms that moved into this region maintaining their original organization.
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Mesoscale, Supercell, MCS, convective mode, Thunderstorm, severe weather, mesoscale convective system
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MS
Discipline
Marine, Earth and Atmospheric Sciences
