Fine-scale Airborne Doppler Radar Measurements of Vertical Air Motions within Lake-effect Systems

Understanding the vertical air motions and vertical structure of lake-effect systems is imperative given the high-impact weather that often occurs within them. To develop a better understanding of these lake-effect systems, airborne Doppler radar data were collected by the Wyoming Cloud Radar (WCR) aboard the University of Wyoming King Air (UWKA) in 20 lake-effect systems near Lake Ontario during the 2013-2014 winter season as a part of the Ontario Winter Lake-effect Systems (OWLeS) project. Improved knowledge of these systems will enhance the prediction of the initiation, demise, movement, and intensity of them.

The fine-scale 15-m resolution of the WCR enables the detection of mesoscale phenomena within these lake-effect systems, including: Cloud top generating cells; deep convective updrafts surrounding the core of the lake-effect bands; gravity waves; Kelvin-Helmholtz waves; and orographic ascent, most notably along the shoreline of Lake Ontario and on the windward side of both the Tug Hill and Adirondack Mountains. Of major focus in this study are the numerous instances of generating cells observed at or near the top of the clouds within several of these lake-effect systems. Within the WCR reflectivity (Z_H) observations, these generating cells exhibit vertical turret-like characteristics with local maximums in Z_H from which fall streaks originate owing to the presence of vertical wind shear. Enclosed within these local Z_H maximums are updrafts on the order of 1-2 m s^-1, while adjacent downdrafts are on the order of 1-3 m s^-1.

A series of case studies is presented. Contoured frequency by altitude diagrams (CFADs) are utilized to exhibit distributions of vertical radial velocity measured by the WCR and to associate the measured vertical radial velocities to vertical air motions within the lake-effect systems. Moreover, a discussion of the commonality of generating cells in lake-effect systems, when they occur (night or day), the synoptic and thermodynamic environments in which they are most common, and the archetype of convection (smaller convective cells or larger mesoscale bands) and band organization (single or multiple band) are discussed. Ancillary information from dual-polarization X-band Doppler radar, ground-based vertically pointing X-band Doppler radar, rawinsondes, and microphysical, kinematic, and thermodynamic data from the UWKA are included when available.