The Structure and Evolution of a Continental Winter Cyclone. Part II: Frontal Forcing of an Extreme Snow Event

Abstract

The production of a narrow, heavy, occasionally convective snowband that fell within a modest surface cyclone on 19 January 1995 is examined using gridded model output from a successful numerical simulation performed using the University of Wisconsin-Nonhydrostatic Modeling System. It is found that the snowband was produced by a thermally direct vertical circulation forced by significant lower-tropospheric warm frontogenesis in the presence of across-front effective static stability differences as measured in terms of the equivalent potential vorticity (PV e ). The sometimes convective nature of the snowband resulted from the development of freely convective motions forced by frontal lifting of the environmental stratification.