Selected Cases of Convective Precipitation Caused by the Metropolitan Area of Washington, D.C.

Abstract

The release of isolated summer showers in the Washington D.C. area, as related to the urban heat island, was studied for nine propitious synoptic situations in 1968, 1972 and 1973. Parcel theory, using urban surface temperature and upper air soundings, permitted comparison between predicted and observed cloud behavior. In all cases the urban thermal effect seemed to be the likely trigger force for shower development. Vertical wind data and cloud energetics permitted an estimate of rainfall positioning in the metropolitan area. In eight of the nine cases, this yielded the correct placing of the urban-induced showers. The study further documents this type of inadvertent rainfall augmentation. Three cases are presented here.