Spatial and Temporal Characteristics of Extreme Rainstorms over the Central United States

A storm catalog was created to illustrate the spatial and temporal characteristics of extremes over the central United States. The catalog contains 57 extreme rainstorms that produced more than 285 mm of rainfall within two days from 1950 to 2000. The storms were classified on the basis of pre-storm conditions using Maddox's classification scheme for flash floods. The majority of the events are mesohigh and frontal events, suggesting that mesoscale forcing is crucial for generating extremes in the central United States.

The distribution of extreme rainstorms is not uniform in space. Two clusters were observed. One is located in the region of Arkansas and Oklahoma, and the other is located near the boundary of Nebraska, Iowa, Missouri, and Kansas. Further analysis shows that mesoscale convective complex (MCC) may be a dominate mesoscale system for generating extreme rainstorms over the central United States, which is consistent with the observations by others. However, our analysis also finds that the clustering of the extremes and the large percentage of total annual MCC rainfall near the boundary of Nebraska, Iowa, Missouri, and Kansas may be related to the Great Plains low-level jet.

For the temporal analysis, extreme rainstorms occurred more frequently in the last 20 years. The occurrence of the extremes depends on season and storm type. Extreme rainstorms occur more frequently in mid-summer, early fall, and late spring. Synoptic events occur mostly in the cool season (from October to March), in contrast to frontal events in the warm season (from April to September). The monthly distributions of synoptic and frontal types extreme rainstorms are similar to those observed by Maddox et al. for flash floods. However, the monthly distribution of mesohigh extreme rainstorms shows distinct characteristics.