An Analysis of Precipitation Transition and Hydrometeor Classification using Dual Polarization Radar and Active/Passive Atmospheric Profiling Observations

An Arctic air outbreak in the days leading up to the winter storm event of February 20, 2015 over Northern Alabama helped set the stage for the anomalously cold surface temperatures that played an important role in multiple precipitation transitions that occurred. Observations are analyzed from the C-Band Dual Polarization ARMOR radar referencing potential thresholds for polarimetric variables and various ice crystal habits from Andric et al. 2013 and Griffin et al. 2014. Furthermore, observations from the Mobile Integrated Profiling System (MIPS) 915 MHz Wind Profiler (915), Microwave Profiling Radiometer (MPR), ceilometer, and surface data are integrated with the ARMOR radar data to determine precipitation transition times and hydrometeor types at the surface and aloft using estimates of hydrometeor terminal fall speed from the 915 spectra (moments) and vertically integrated liquid from the MPR. The analysis is compared with verification observations from all available surface data and local storm reports. For this event, a transition from snow to a mixture of sleet and ice crystals to freezing rain occurred over a four hour time period. Among the hydrometeors identified are dendrites, snowflakes, planar crystals, aggregates, sleet, and freezing rain.