The Wyoming King Air research aircraft and airborne millimeter-wave cloud radar were used to examine the evolution of precipitation particle size distributions in several deep, wintertime nimbostratus in southeastern Wyoming and northeastern Colorado. In each case the airplane was flown in a series of descending spirals at a constant descent rate of 1 m/s and was allowed to drift with the prevailing winds, thus approximating a Lagrangian sampling of the falling precipitation. In two cases (April 19 and Nov. 5, 2000) the size distribution changes were dominated by aggregation. In another (April 22, 2000) the changes were dominated by evaporation. Interestingly, the size distribution changes on April 22 suggest that aggregation growth may have continued in the midst of evaporation throughout the 3500-m vertical extent of the measurements. For each case the particle size evolution will be examined within the context of the horizontal and vertical radar reflectivity patterns, and will also be compared with results from earlier studies.