This presentation will focus on the locations of heavy rain development and climatic trends in frequencies of heavy rain events for a range of urban centers located close to large rivers in the US Midwest. Heavy rain initiation frequencies were quantified by identifying the development of precipitation with at least 35dBZ radar reflectivity as observed by the NOAA WSR-88D network. Long-term trends in heavy rain frequencies were determined using NOAA surface-based daily precipitation sites and multi-sensor precipitation fields.
It was found that heavy rains initiated nearly twice as often over a five-year period (2009-2013) within a 40-km diameter circle encompassing the St. Louis urban land-use area than over an equal-sized nearby rural area. Mid-sized urban areas (Terre Haute, IN, and Davenport, IA) experienced storm initiation frequencies between those for the St. Louis and rural areas. Areas of maximum daily rainfall frequencies greater than 2.5, 5.1 and 7.6 cm typically extended from over the urban areas to within about 100 km of the urban centers.