Structural Evolution of a Warm Frontal Precipitation Band During the GPM Cold-Season Precipitation Experiment (GCPEx)
On 18 February 2012 a surface warm front was approaching southern Ontario ahead of a relatively weak cyclone. A well-defined warm frontal precipitation band developed just north of the surface front, which intensified and narrowed rapidly as it moved northward. Initially, the band was fairly broad and was associated with dry snow with little super-cooled water. An hour or two later by its mature phase there was a narrow plume of more aggregated snow, with significant riming on the south side of the band. There were also numerous small-scale gravity wave perturbations near the band and convective cells aloft as revealed by the high-resolution radar data. This presentation will summarize the structural evolution of this band as well as some factors that led to its intensification, which includes the development of a low-level jet, mid-level dry intrusion, and frontogentical forcing. This event was also simulated down to 1-km grid spacing using the Weather Research and Forecasting (WRF) model. The WRF was able to realistically simulate the warm frontal band development and some of its intensification characteristics, so the simulation is used to complement the observations with understanding the evolution of this case.