A comparison of mesoscale band life cycle during three recent northeast U.S. snowstorms

Mesoscale snowbands are frequently observed in the comma-head portion of extratropical cyclones in the eastern United States. The advent of Doppler radar, wind profilers, frequent aircraft soundings, and ground-based integrated precipitable water vapor sensors has allowed unique measurements in the vicinity of such bands. Concurrently, high-resolution models such as the MM5 and WRF models have shown the capability to predict band formation and evolution. This study uses various observational platforms and high-resolution versions of the MM5 and WRF models to compare the dynamics of mesoscale band life cycle during the 25 December 2002, 12 February 2006, and 14 February 2007 northeast U.S. snowstorms, and to assess the performance of high-resolution models in forecasting these banded events.

In all three snowstorms observations show band formation was coincident with the sharpening of a midlevel trough and associated increase in frontogenesis in an environment of conditional, slantwise, and inertial instability. Band dissipation occurred as the midlevel trough became more diffuse, weakening the associated frontogenetical forcing, while the stability increased. Potential Vorticity (PV) analysis in each case showed that the bands formed within a region of maximum positive PV advection on the dynamic tropopause. This advection weakened during band dissipation, consistent with weakening forcing for ascent. Changes in moisture availability in the banded region during the respective band life cycles were small, suggesting changes in the forcing and stability were the primary governors of band lifecycle in these three northeast U.S. snowstorms.

Band formation was forecast by high-resolution versions of the MM5 and WRF in all three snowstorms; however, the forecasts exhibited band location and evolution errors. Also, a clear under prediction of precipitation was noted in the 25 December 2002 and 12 February 2006 snowstorms. Possible reasons for these model errors will be presented at the conference. Particular focus will be placed on identifying differences between observations and model forecasts of the evolution of the environmental stability and frontogenesis in the vicinity of the bands.