On the 2013 Spring Floods at Chicago

Probably the worst floods experienced by Chicago area residents in the last three decades occurred this past spring: On 2013 April 18th, Illinois was declared in a State of Emergency, and by April 21st, forty four of its counties were declared as Disaster Areas. This work will describe the precipitation conditions of this flood in a unique way.

For characterizing some of the precipitation microphysical features of the event, we analyze data collected at Argonne's weather observatory. The monitoring equipment includes a 915-MHz profiler radar, co-located with a 24-GHz vertically-pointing radar (Micro-Rain-Radar2), a Parsivel2 disdrometer, conventional weather sensors on a 60m tower, and conventional raingauges at the ground. Hydrological estimates (such as rainfall rate maps) are then obtained by combining these observations with the measurements of a scanning weather radar nearby (the LOT WSR-88D at Joliet IL, featuring S-band and Dual-polarization). For characterizing the mesoscale features of the event, the Weather Research and Forecasting model (WRF, version 3.3.1) was implemented to estimate various meteorological analysis fields at very high resolutions (in the order of 1 km horizontally and 10-mininutes in time). These computations use initial and boundary conditions derived from operational NCEP reanalysis (resolutions of one degree horizontally and 6 hours in time). The results provide a detailed depiction of the thermodynamic structure of the weather system associated to the flood event. Finally, we summarize the study by analyzing 1km-constant-altitude composites of rainfall accumulation, from the six WSR-88D weather radars nearby, with the very-high-resolution WRF fields overlaid.

The integration of these radar and simulation platforms near a large city (such as Chicago) during a high impact weather event (such as these record-breaking floods) is quite remarkable, and it opens new doors for developing useful precipitation and hydrologic applications in the urban context.