Mesoscale and Microphysical Characteristics of Elevated Convection and Banded Precipitation over an Arctic Cold Front: A Case Study from IMPACTS

The mesoscale and microphysical structure of a cloud system associated with an Arctic front is analyzed using data from two research aircraft, two WSR-88D radars, the HYSPLIT model, and initialization fields from the RAP model. The flights, conducted during the NASA Investigation of Microphysics and Precipitation in Atlantic CoastThreatening Snowstorms (IMPACTS) campaign, collected in situ and remote sensing data as the cloud system moved across Illinois. The system developed within an air mass that, based on back trajectory analysis, originated over the subtropical eastern Pacific before being lifted over the Arctic front. This led to a region of potential instability extending upward over the frontal zone. The ascending flow triggered the release of the instability that manifested as elevated convection in the storm’s southern sector. In the convective region, supercooled water was found in cloud towers, leading to saturated conditions that supported growth of a range of particle habits and growth by riming. Within this region, and in shallower clouds between convective towers, needle particle habits, supercooled water, and high ice particle concentrations implied active secondary ice processes. Two snowbands formed north of the convective region, with radar evidence suggesting that precipitation within these bands originated in cloud towers at altitudes of 4–6 km in a near-neutral to weakly unstable region. Water saturated conditions, evidenced by supercooled water at the sampling level, permitted the growth of a range of particle habits. Despite ice particle concentrations < 15 L^-1 within the bands, some aggregated particles exceeding a centimeter in maximum dimension were observed at-58C, likely contributing to the 21–27 dBZ_e reflectivity characteristic of the bands.