2.2 The Evolution of Mesoscylcones and Tornadic Development Under Different Shear Profiles

Monday, 4 October 2004: 1:45 PM
Philip N. Schumacher, NOAA/NWS, Sioux Falls, SD; and J. M. Boustead and J. A. Chapman

On 24 June 2003, approximately 100 tornadoes were reported in eastern South Dakota, southern Minnesota, northwestern Iowa, and northeastern Nebraska. Through use of profiler, radar and model data, it was seen that three different shear profiles existed across southeast South Dakota during the afternoon and evening. Tornadoes were observed within all three environments. The first shear profile was typical of a classic supercell profile with turning in the lowest 3 km and acceleration of the flow above 3 km. The result was the development of isolated classic supercells with several large tornadoes reported. The second shear profile had large acceleration of flow in the lowest 1 km of the atmosphere with anticyclonic shear existing between 3 and 6 km. This shear, combined with large low-level instability, resulted in the numerous short-lived weak tornadoes. Several of these storms also developed meso-anticyclones which moved to the left of the mean wind and produced large hail later in their life cycle. The final shear profile favored the development of high precipitation (HP) supercells. The storms that developed in this environment formed a squall with rapid development of low level mesocyclones and tornadoes as the squall line began to mature.

An examination of the development and evolution of mesocyclones from inception through dissipation will be done for each shear profile. Through plotting of mesocyclone strength and depth for representative storms within each environment, we will show that mesoscale differences in the environmental shear resulted in markedly different storm evolutions for storms that formed within 100 km of each other. Understanding and monitoring of shear before and during potential tornado outbreaks is critical for forecasters to anticipate the very different evolutions of mesocyclones which can lead to large hail, damaging winds, and tornadoes.

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