Mesoscale Structure in the Megalopolitan Snowstorm, 11–12 February 1983. Part II: Doppler Radar Study of the New England Snowband

Frederick Sanders Center for Meteorology and Physical Oceanography, Massachusetts Institute of Technology, Cambridge, MA 02139

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Lance F. Bosart Department of Atmospheric Science, State University of New York at Albany, Albany, NY 12222

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Abstract

A major snowstorm in eastern Massachusetts, 11–12 February 1983, was associated with a persistent mesoscale band of high reflectivity observed at MIT. The band was strengthened, then weakened, by the propagation of a high-amplitude gravity wave through it, without permanent disruption of either entity. Transformation of a single band to a group of three accompanied rotation from zonal to northeast-southwest, as the storm passed eastward out of radar range.

An RHI cross section normal to the band at the inception of breakup showed a shallow layer of strong transverse (warm-to-cold) velocity components, evidently due to large-scale frontogenetical forcing, separating ascending air with small hydrostatic and symmetric stability above from descending air with large stability below. Band breakup was associated with a prominent small-scale oscillation along transverse jet

Vertical motions calculated from a velocity azimuth display time series showed descent in the layer from 1.5 to 2.5 km throughout the storm, with strong ascent and condensation present only well aloft. The storm-total overhead condensation, nevertheless closely with the storm-total snowfall.

Prominent fluctuation in the ascent reflected the passage of the gravity wave. Further unsteadiness of the ascent, and the breakup of the band, may have been attributable to symmetric instability.

Abstract

A major snowstorm in eastern Massachusetts, 11–12 February 1983, was associated with a persistent mesoscale band of high reflectivity observed at MIT. The band was strengthened, then weakened, by the propagation of a high-amplitude gravity wave through it, without permanent disruption of either entity. Transformation of a single band to a group of three accompanied rotation from zonal to northeast-southwest, as the storm passed eastward out of radar range.

An RHI cross section normal to the band at the inception of breakup showed a shallow layer of strong transverse (warm-to-cold) velocity components, evidently due to large-scale frontogenetical forcing, separating ascending air with small hydrostatic and symmetric stability above from descending air with large stability below. Band breakup was associated with a prominent small-scale oscillation along transverse jet

Vertical motions calculated from a velocity azimuth display time series showed descent in the layer from 1.5 to 2.5 km throughout the storm, with strong ascent and condensation present only well aloft. The storm-total overhead condensation, nevertheless closely with the storm-total snowfall.

Prominent fluctuation in the ascent reflected the passage of the gravity wave. Further unsteadiness of the ascent, and the breakup of the band, may have been attributable to symmetric instability.

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