Thorndahl, Søren1; Smith, James A.6; Baeck, Mary Lynn6; Krajewski, Witold F.7
1 Department of Civil Engineering, The Faculty of Engineering and Science, Aalborg University, VBN2 Division of Water and Soil, The Faculty of Engineering and Science, Aalborg University, VBN3 Urban Water and Environment Research Group, The Faculty of Engineering and Science, Aalborg University, VBN4 Water and Environment Research Group, The Faculty of Engineering and Science, Aalborg University, VBN5 The Faculty of Engineering and Science (ENG), Aalborg University, VBN6 Princeton University, Department of Civil and Environmental Engineering, Princeton, NJ7 The University of Iowa, IIHR - Hydroscience and Engineering, Iowa City, IA
In this paper, we develop a storm catalog of heavy rainfall events for a region centered on the Milwaukee, Wisconsin WSR-88D (Weather Surveillance Radar – 1988 Doppler) radar. The study region includes portions of southern Wisconsin, northern Illinois and Lake Michigan. The long-term objective of this study is to develop rainfall frequency analysis methods based on a storm catalog of major rain events. The specific objectives of this study are to develop a long-term catalog of high-resolution radar rainfall fields and characterize key features of the space-time variability of rainfall. The research questions that underlie these objectives are: 1) what are the spatial heterogeneities of rainfall over the study region for major flood-producing storm systems? 2) what are the key elements of storm evolution that control the scale-dependent properties of extreme rainfall? The storm catalog contains a record of the 50 “largest” storm days during the 1996 – 2011 observation period. We show that mean rainfall for the 50 largest storm days exhibits pronounced spatial heterogeneity with a broad maximum in western Wisconsin and a minimum in the eastern portion of the study region over Lake Michigan. We also show that there is a narrow line of maximum mean rainfall extending from west to east along the Wisconsin-Illinois border. This feature is tied to a maximum in the probability of daily rainfall exceeding 100 mm. There are characteristic elements to the storm life cycle of heavy rainfall days that relate to size, structure and evolution of heavy rainfall. Extreme rainfall is also linked with severe weather (tornados, large hail and damaging wind). The diurnal cycle of rainfall for heavy rain days is characterized by an early peak in the largest rainfall rates, an afternoon-evening peak in rain area exceeding 25 mm h− 1 and development of a large stratiform rain area during the night and early morning.
Atmospheric Research, 2014, Vol 144
Heavy rainfall; NEXRAD; Radar rainfall; Temporal and Spatial Structures; Hydrometeorology