Radar and profiling observations of the interaction between a lake effect snow band and a shallow cold front during the Ontario Winter Lake-effect Systems (OWLeS) Experiment

The Ontario Winter Lake-Effect Systems Experiment was conducted during December 2013-January 2014. The project utilized in-situ and remotely-sensing instruments in order to obtain small-scale and large-scale kinematic and thermodynamic measurements of lake-effect snow bands. This paper presents a multi-sensor analysis of a Long-Lake Axis Parallel (LLAP) Band on 15-16 December 2013. Multiple ground-based and in situ measurements were collected during the Intensive Observational Periods (IOPs) by various fixed and mobile sensors, including: multiple radiosondes, the Center for Severe Weather Research (CSWR) weather pods and mesonets, Doppler On Wheels (DOW) 6, DOW 7, & DOW 8, the University of Wyoming King Air (UWKA), and the University of Alabama in Huntsville (UAH) Mobile Integrated Profiling System (MIPS). The band initially formed and stayed relatively stationary near the MIPS, before moving northward. Subsequently the band narrowed and intensified, followed by a southward movement after a southward-moving cold front oriented nearly parallel to the band interacted with it. Dual-Doppler analyses were conducted between 0550-0626 UTC on 16 December to document the band evolution prior to moving over the MIPS, which was located near the southern shore of Lake Ontario. Both DOW radars (DOW 6 & DOW 7) documented misovortices along the leading edge of the band/cold front. RHI scans revealed a sharp cold frontal boundary with a head about 1.5 km deep resembling a density current embedded within the band. The MIPS instruments appear to have captured the passage of one of these misovortices between 0610-0615 UTC. The MIPS's 915 MHz Wind Profiler recorded a vertical motion couplet around 0613 UTC, first with a 4-5 m/s updraft, followed immediately by a 2-3 m/s downdraft. Many high resolution structures (5-6 m/s updraft and 3-5 m/s downdraft) within this couplet were documented by the MIPS X-Band Profiling Radar (XPR) around 0613-0614 UTC. Stronger updrafts were documented in the upper regions of this 3 km deep band, including the highest updraft magnitude of 12 m/s sampled by the XPR during the project. The DOW 7 RHI scans of the passage of the shallow cold front showed ZDR values of 0.1-1.0 dB, which is indicative of dry snow and/or aggregated ice crystals as the primary precipitation particle present in this event. The dual-pol observations are combined with the detailed kinematic, thermodynamic, and microphysical information provided by the MIPS profiling instruments.