Mesoscale Structure in the Megalopolitan Snowstorm of 11–12 February 1983. Part I: Frontogenetical Forcing and Symmetric Instability

Abstract

Abstract A cyclone moving northeastward off the coast of the northeastern United States on 11–12 February 1983 was accompanied by a band of heavy snow across all the major cities of this region from Washington to Boston. Frontegenetical forcing and symmetric instability are discussed as possible explanations of the intense precipitation. Rawinsonde data were analyzed to investigate the roles of these effects in this case. We found that intense ascent was part of a thermally direct transverse circulation, to be expected in response to frontogenetical forcing when the symmetric stability in the warmer air is small. Symmetric instability per se in the saturated major cloud mass may have been responsible for pulselike oscillations in its top. These were men in satellite imagery, elongated in the direction of the tropospheric thermal wind.