Lyza, et al. p.1 A C-Band, Dual-Polarimetric Radar Analysis of a Tornadic Mesoscale Convective System: The 25 May 2011 Northern Illinois and Indiana Tornado Event Anthony W. Lyza 1* , Raquel Evaristo 1 , Eric Lenning 2 , Sarah K. Mustered 1 , Travis J. Elless 1 , Sarah A. Al- Momar 1 , Ian R. Lee 1 , Teresa M. Bals-Elsholz 1 , Bart J. Wolf 1 , Kevin H. Goebbert 1 , Adam J. Stepanek 1 , and Craig A. Clark 1 1 Valparaiso University, Valparaiso, Indiana 2 National Weather Service Forecast Office, Chicago/Romeoville, Illinois ABSTRACT During the morning hours of 25 May 2011, at least six tornadoes struck a narrow corridor of Northeast Illinois and Northwest Indiana. Two tornadoes were rated EF0, three EF1, and one EF2. These tornadoes occurred in conjunction with a mesoscale convective system (MCS) that traveled northeast across the region during the early to mid-morning hours, between 1200 UTC and 1500 UTC. The tornadoes occurred at least 65 km away from the nearest NEXRAD WSR-88D radar site. The confirmed tornadoes from this event occurred without severe thunderstorm or tornado warnings likely due to the fact that, (1) the squall-line was oriented parallel to the radar beam, (2) there were minimal real-time spotter reports, (3) embedded circulations were shallow, and (4) the tornado producing storms did not exhibit classic radar signatures at the nearest NEXRAD locations. The tornadoes occurred approximately 50-75 km from the C-band dual-polarimetric radar located on the campus of Valparaiso University in Valparaiso, IN. In this presentation, we examine the data gathered from the C-band, dual-polarimetric radar at Valparaiso University. We review the data in order to reveal methods that could have better detected the tornadoes produced during this event. . 1. Introduction Valparaiso University operates a 5-cm wavelength, simultaneous dual-polarimetric radar (VU-SIDPOL) located on the university campus in Porter County, Indiana, approximately 65 km southeast of Chicago. Built in 2007, the radar is primarily used in conjunction with radiosonde data gathered by university students for the Massachusetts Institute of Technology’s Lincoln Laboratory (MIT-LL), through a joint project with the Federal Aviation Administration (FAA) to study icing hazards for commercial aircraft and aid in the development of an icing algorithm for the National Weather Service (NWS). Additionally, the VU-SIDPOL radar is useful in the detection of storm-scale circulations. Past research has included the detection of an EF1- * Corresponding author address: Anthony W. Lyza, 1509 Chapel Dr. Unit 1381, Valparaiso, IN 46383 E-mail: tony.lyza@valpo.edu rated tornado that occurred on 26 October 2010 approximately 15 km from the radar (Evaristo et al. 2011). In the 2010 case, the VU-SIDPOL radar was useful in detecting a tornado debris signature (TDS) in the cross-correlation coefficient (ρ hv ) moment, with a minimum ρ hv of 0.48 observed in association with the tornadic mesovortex. Another opportunity for studying tornadic circulations with the VU-SIDPOL radar occurred on 25 May 2011. In this case, a remnant quasi- linear convective system (QLCS) from a tornado outbreak in the southern plains on 24 May 2011 moved northeast across central Illinois and into northwestern Indiana, producing at least eight tornadoes, six of which occurred in northeast Illinois or northwest Indiana. These tornadoes ranged in intensity from EF0 to EF2 intensity and caused isolated but locally significant damage. This tornado event was not well-anticipated, as most of the focus was on the potential for a more widespread tornado outbreak in the afternoon and evening hours. National Weather Service records from the Lincoln (ILX), Chicago/Romeoville (LOT),