Hydroclimatological characteristics of isolated severe rainstorms

Abstract

Intense but very localized severe rainstorms are the most frequent type of flash flood‐producing rainstorms in the United States. These storms often go unmeasured because the nation's raingage network is too sparse. A well‐measured sample of 32 storms was obtained from operations of dense raingage networks in Illinois. These storms typically last from 3 to 12 hours, affect less than 1000 km 2 , and have 1‐ to 4‐hour rainfall totals in excess of 7.5 cm. Area frequency relationships indicate about 40 of these storms occur during each warm season over Illinois, an area of 145,000 km 2 . The morphology of one severe isolated rainstorm is described to illustrate the typical conditions. The heavy rains (>17 cm) from this storm fell within both urban and rural regions, causing extensive damage. The heavy rain was due to a succession of moderately intense small individual storms that moved across the same region. Real‐time detection of such storms is possible from careful observations of radar data.