Precipitation type characteristics at the surface in winter storms

The precipitation characteristics across the precipitation type transition regions of several Canadian East Coast winter storms were studied using the unique data collected during the CASP field experiment in 1986. Regardless of whether the precipitation was freezing rain, rain, ice pellets or snow, particle size spectra information generally revealed exponential distributions but deviations from these were common. Using a sophisticated microphysical numerical model and observed winds and temperatures, precipitation particle trajectories were computed through the lower troposphere in order to predict, for the first time, the detailed nature of surface precipitation types. Comparisons with observations were sometimes good although problems still exist. Furthermore, varying particle trajectories in the transition region lead to significant variations in precipitation rate and alter the spatial distribution of the precipitation types.