1. Inadvertent Weather Modification The Urban Heat Island The METROMEX project St. Louis, MO http://www.arrakeen.ch/usaaug98/110%20%20St.Louis.JPG

2. The Urban Heat Island Produced by the combined effects of –Heat Capacity –Albedo –Heat Generation –Radiative Heating and Cooling Rates –Surface Roughness Is this really weather modification?!

3. METROMEX Metropolitan Meteorological Experiment –Studied the areas around St. Louis in the summers of 1971-1975 Goals: –Identify effects of urbanization on atmospheric behavior (i.e. precipitation and severe weather –Identify physical process through which observed effects are produced –Identify the factors of urbanization which cause these effects

4. From Changnon, et al., 1971

7. From Project METROMEX, 1974 (BAMS)

8. 1. For cells originating in the St. Louis urban area, rainfall volume average was 216% greater than control sample. 2. For cells originating in the Alton-Wood River urban area, rainfall average was 289% greater than contral sample. 3. Convective initiation zones was more likely to found in the industrial areas

9. From Project METROMEX, 1974 (BAMS)

17. Summary Large Industrial/Urban areas favor –Higher temperatures –Increased rainfall downwind –Increased hailfall downwind –Differing microphysical precipitation process downwind –Higher convective cloud bases due to increased boundary layer height