Characteristics of cloud ice and precipitation during wintertime storms over the mountains of northern Colorado

The region of the cloud near cloud top was found to be a primary source region for ice particles in these clouds. Ice particle concentrations were found to increase over elevated topography and to increase at lower altitudes in deep cloud systems. The activity of three secondary ice particle production mechanisms was evaluated. Fragmentation was found to be important in cloud systems that contained dendritic crystals. Evidence suggested that the Hallett-Mossop rime splintering mechanism occurred only occasionally in these clouds and contributed little to the total precipitation. Droplet fragmentation during freezing did not appear to be an important mechanism. The primary components of aggregates in Park Range cloud systems were planar dendritic crystals and radiating assemblages of dendrites. When these particles were present in the snowfalls, aggregation occurred independent of surface temperature and precipitation rate. Significant aggregation was not observed when dendritic crystals were not present. -from Author