Evolution of downdrafts and rotation in an Illinois thunderstorm

Multiple-Doppler radar observations of a non-severe Illinois thunderstorm with nearly rectilinear vertical wind shear and storm motion related to the wind at a height of 2.5 km are discussed. The cell examined had a radar top of 10 km, and reflectivities of 60 dB(Z). Attention is given the evolution of updraft, downdrafts, and vorticity in this cell, where typical magnitudes were 12 m/sec, 8 m/sec and 0.005/sec, respectively. The main downdrafts were found to be the upshear downdraft during the growth period of the cell, and the left bank downdraft during the mature and downdraft periods. The location of upshear downdraft at mid to upper levels resembles the Lennon and Doswell (1979) conceptual model, as well as three-dimensional cloud model results of severe storms.