There is a very informative communication by J. Marshall Shepard of the University of Georgia Department of Geography and Atmospheric Sciences with respect to urban effects on thunderstorm activity. He has summarized this finding in the communication below.
Guest Post By J. Marshall Shepherd
I put together this qt movie sequence of the Atlanta radar for Thursday May 27 2010 that illustrates a 4 to 5 hour sequence in which thunderstorms were repeatedly forming over south Atlanta/airport area and drifting to the SW with the prevailing flow out of the NE. Notice how the storms just continue to re-generate over the area mentioned. This is a really nice example of urban-initiated storms. Also, notice how the outflow boundaries from those storms really get things going further in the downwind region. Very impressive sequence.