Professor Cotton's major research focus is on the investigation of convective storms and mesoscale systems -- their dynamics, precipitation formation, and their predictability. Both observational and numerical modeling approaches are used in investigating these storms. Jointly with Dr. Pielke, he has developed the Regional Atmospheric Modeling Systems (RAMS) which is a sophisticated interactive, nested grid model capable of explicitly simulating clouds and storms as well as a variety of mesoscale phenomena. Under his direction, RAMS is also being applied to the large eddy simulation of the cloudy boundary layer, the simulation of cirrus clouds, dynamics and microphysics of convective storms including tornadoes, hailstorms, and derechos, the numerical prediction of agricultural, aviation impact variables and precipitation, to extreme precipitation estimation, indirect effects of aerosols on climate, and urban influences on regional climate.