Airborne Radar Observations and Model Analysis of a Secondary Circulation within a Shallow Lake-Effect Snow Band

Narrow, intense lake-effect snow bands are commonly observed over Lake Ontario during wintertime cold-air outbreaks. These bands often become quite deep when the prevailing flow is out of the west, more or less parallel to the long axis of the lake, and may be enhanced (and perhaps maintained) by a deep secondary circulation. On 7 January 2014, a long-lived lake-effect snow band developed over Lake Ontario during a particularly strong cold air outbreak and persisted for almost 72 hrs. The band was deepest (almost 3 km) and most intense early in the event when the prevailing flow was more favorably aligned (i.e., out of the west or southwest) with the long axis of the lake. However, this study examines the band late in its life on 9 January when it was weaker and shallower, and when the prevailing flow had shifted to northwesterly. Airborne dual-Doppler observations from the Wyoming Cloud Radar (WCR) reveal that the band was only ~1.6 km deep at this time, too shallow to be detected by the closest operational National Weather Service radar. The dual-Doppler observations also show the presence of a well-organized secondary circulation within the band and a very shallow (~0.5 km in depth) inflow layer that was likely associated with a land breeze. High resolution Weather Research and Forecasting (WRF) model output show fairly good agreement with the radar observations and provides support for the presence of a land breeze near the southern shoreline of the lake. Furthermore, the model indicates the presence of two prominent convergence lines: the first stretching out over the lake coinciding with the position of the band, and the second oriented obliquely to the first near the southeast shoreline in association with the leading edge of the apparent land breeze.