Combined Polarimetric and Multiple Doppler Radar Observations of the 16-20 March 2003 Colorado Area Winter Storm

During the second week of March 2003, a winter storm of historic proportions (maximum storm total snow accumulations exceeding 200 cm) struck large areas of Colorado and southern Wyoming. The CSU CHILL and Pawnee research radar systems conducted volume scans that were synchronized at 10 minute time intervals over a 50 hour period during which the great majority of the storm's precipitation fell. To provide additional insights into the microphysics of the precipitation, the CSU-CHILL radar was operated in dual polarization (alternating H and V transmit polarization) mode, and executed periodic RHI scans during the data collection period.

A northerly barrier jet flow at heights below ~3 km MSL in the area immediately east of the Rocky Mountain foothills was found to be a prominent feature in the dual Doppler horizontal wind field syntheses. Above the barrier jet, the average wind direction was generally easterly. The differential reflectivity (Z_dr) and specific propagation differential phase (K_dp) values tended to be positive in the easterly flow layer aloft; indicative of the presence of ice particles that were generally oriented with their major axes in the horizontal plane. However, within the higher reflectivity regions within this flow, Z_dr and K_dp tended to near zero, consistent with ice particle aggregation. Reflectivity “streamers” were evident from these enhanced regions of reflectivity which apparently generated banded low level echo features as they fell into the underlying barrier jet flow. This paper will document the evolution of selected mesoscale echo features during particularly active phases of the overall winter storm.