Investigation of Multi-bands in the Comma Head of the 26-27 December 2010 Northeast U.S. Winter Storm

Mesoscale precipitation structures within Northeast U.S. winter storms result in heterogeneous spatial and temporal snowfall throughout the region during any one particular storm. There have been many studies of single-banded snowbands in the comma head, and several successful modeling studies of these bands, but fewer studies of multi-banded events. Multi-bands are defined as > 3 finescale (5–20 km width) bands with periodic spacing and similar spatial orientation maintained for at least 1 h. While multi-bands have been observed to be more transient and shorter-lived structures than single bands, they are capable of producing similar enhanced snowfall rates and wind speeds. The Northeast U.S. blizzard of 26-27 December 2010, also known as the “Boxing Day Storm,” was an exemplary case of multi-banding. This poster will examine the processes resulting in the genesis, maturity, and decay of the multi-bands by employing available observations and 1.33-km horizontal grid spacing output from a representative Weather Research and Forecasting (WRF) simulation. Analysis of the velocity data from the observational radar network shows that there is gravity wave activity extending through some depth of the lower troposphere that travels at a faster rate than the precipitation cells and bands.  In both the observations and WRF simulations many of the multi-bands correspond with these waves sometime during the band life cycle, and both waves and bands develop in the same general region offshore, but not all waves have corresponding bands. The simulated bands were associated with low-level potential vorticity maxima and associated convective cells that existed before band development, which then organized parallel to the shear vector and a weak deformation axis. This suggests that pre-existing convective cells (and associated PV anomalies) may be important in the subsequent evolution of the multi-bands. The triggering mechanism for the convective cells and subsequent bands is thought to be gravity wave activity, shear-induced circulations, or forcing via a weak frontal zone.