Heavy rainfall: Contrasting two concurrent great plains thunderstorms

Measurement and forecasting of heavy rainfall requires interpretation of the small differences in the storm environment that distinguish a major flood-producing rainfall event from a relatively harmless storm system. This case study will examine some of the small differences in the storm environment that lead to a heavy rainfall event. On 8 July 1994 two storm systems developed in close proximity to each other in central Oklahoma. One of the storms developed into a squall line and produced low storm total precipitation accumulations. The other was a slow-moving multicellular storm that produced storm total precipitation of more than 130 mm and small stream flooding. The storms exhibited contrasting measurement errors in the operational WSR-88D rainfall products, with underestimation for the heavy rain event and overestimation for the squall line. The interactions of synoptic, mesoscale, and storm-scale processes for the 8 July storms are examined through analyses of WSR-88D reflectivity and Doppler velocity observations, surface and upper-air observations from the GEWEX-GCIP Integrated Systems Test experiment, and GOES observations from visible, IR, and water vapor channels. This case study gives a unique opportunity to analyze the differences and similarities of the prestorm environment that lead to different storm structures and rainfall accumulations. Analyses also illustrate storm-scale and mesoscale processes that play a major role in determining the accuracy of WSR-88D rainfall estimates.