Mesoscale Spatial Variability in Midwestern Precipitation

Abstract

Data from four dense raingage networks operated for periods of 7?12yr on areas of 10?550 mi2 in Illinois were used to determine the spatial relative variability of storm, monthly, and extended period precipitation in a continental climate typical of midwestern United States. The relation of storm variability to areal mean precipitation, storm duration, precipitation type, synoptic weather type, season, and size of sampling area was investigated. Storm variability was found to be related exponentially to areal mean precipitation and the relationship was improved only slightly by the addition of storm duration. The storm variability increases with increasing area and is substantially greater with unstable types of precipitation (TRW, RW) than with steady types (R, S). Synoptically, the highest values were obtained with air mass storms and the lowest with low center precipitation. Great interstorm variability was found under apparently similar storm conditions. Monthly precipitation variability is greatest during summer periods of low precipitation, and displays little difference among fall, winter and spring months. When integrated over extended periods, the average spatial variability on an area of 400 mi2 decreased to a constant of 4% for periods of 24 months or longer.