This paper presents an analysis of aircraft measured cloud microphysics data and ground-based polarimetric radar data to identify radar signatures in winter clouds. The data used in this study were collected during the First Alliance Icing Research Study (AIRS I), which was conducted during the 1999-2000 winter months in Quebec, Canada. The main objective of the AIRS I was to characterize aircraft icing environments, particularly those associated with supercooled large drops. The in-situ data used in this study were collected using the National Research Council (NRC) Convair-580 that was instrumented by the Meteorological Service of Canada (MSC) and the NRC. Polarimetric radar data from the McGill University S-band radar and the McMaster University X-band portable radar collected during the aircraft transects over the study area are also used in the analysis. In this study, radar signatures of mixed-phase and glaciated winter clouds are obtained from in-situ microphysics data using the T-matrix scattering model. The in-situ data is subdivided into specific size intervals and particle types. These were used to characterize model inputs (e.g. effective dielectric constant, aspect ratio) and to determine their influence on the computed polarimetric variables. The modeling results were then compared with the two ground-based radar measurements. The in-situ data provided the finely resolved details that can explain the behavior of the observed polarimetric variables. As a result, regions of these winter cloud systems in which microphysical processes are associated with icing conditions were identified.