Observations of freezing drizzle in extratropical cyclonic storms during IMPROVE-2

The storms were characterized by a structure and evolution similar to the split-front model of synoptic storms. Both storms were also characterized by strong cross-barrier flow.

An analysis of aircraft and radar data indicated the presence of supercooled drizzle during two distinct storm periods: 1) the intrafrontal period immediately following the passage of an upper cold front and 2) the postfrontal period. The conditions associated with these regions of supercooled drizzle included 1) temperatures between -3° and -19°C, 2) ice crystal concentrations between 1 and 2 L⁻¹, and 3) bimodal cloud droplet distributions of low concentration [cloud condensation nuclei (CCN) concentration between 20 and 30 cm⁻³ and cloud drop concentration 15 dBZ) in this region, the relatively high condensate supply rate led to hazardous icing conditions.