Heavy snow fell on 18 December 1971 in parts of coastal New England, but not in Boston proper, as intense synoptic-scale cyclogenesis occurred over the Gulf Stream to the southeast. Mesoscale analysis of surface data shows that part of the snowfall was attributable to shallow instability in onshore flow, but that a substantial portion was associated with a small and short-lived cyclone which formed at the mouth of Boston Harbor.

This analysis, together with consideration of the few pertinent upper-level soundings, indicates a similarity between this cyclone and the “polar low” which produces heavy snow in the United Kingdom. The mechanism of this cyclone appears to be qualitatively similar to that of synoptic-scale baroclinic cyclones. Its small size is attributed to the low hydrostatic stability produced by heat flux from the relatively warm water of Massachusetts Bay and to the restricted vertical depth of the associated atmospheric baroclinic zone. There is a remote possibility that a significant part of the heat flux in this case may have been from an anthropogenic source.

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