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A climatological and composite study of banded precipitation in the northeast United States during the cold season (October–April) is presented. Precipitation systems in the northeast United States in April 1995 and from October 1996 to April 2001 that exhibited greater than 25.4 mm (1 in.) of rainfall, or 12.7 mm (0.5 in.) liquid equivalent, were identified as cases for study. A total of 111 cases were identified during this period, of which 88 had available radar data. Of these cases, 75 exhibited banded structure whereas 13 did not. A band classification scheme was developed from a subset of study cases. Application of the classification scheme to the 88 cases revealed that banded cases can exhibit a variety of banded events during their evolution. Single-banded events were the most common (48), followed by transitory (40), narrow cold frontal (36), multi (29), and undefined (9). Further investigation of the single-banded events highlighted banded structure in the comma-head portion of storms, with 81% of these events exhibiting a majority of their length in the northwest quadrant of the surface cyclone. Composites were calculated for cases exhibiting single-banded events in the northwest quadrant of the surface cyclone and for nonbanded cases to distinguish synoptic and mesoscale flow regimes associated with banded events and nonbanded cases. The banded composite was marked by cyclogenesis and the development of a closed midlevel circulation. This flow configuration was associated with deformation and strong midlevel frontogenesis northwest of the surface cyclone center, which coincided with the mean band position. The nonbanded composite exhibited a much weaker cyclone located in the confluent entrance region of an upper-level jet. The absence of a closed midlevel circulation in the nonbanded composite limited deformation and associated frontogenesis northwest of the surface cyclone. Cross-section analysis through the respective composite frontogenesis maxima showed that the banded composite frontal zone exhibited stronger and deeper frontogenesis and weaker conditional stability than the nonbanded composite frontal zone. Case studies from the northeast United States confirm the composite results, highlighting the importance of deep-layer frontogenesis coincident with weak conditional stability. These results are in qualitative agreement with the Sawyer–Eliassen equation, which predicts that the frontogenetical response will be enhanced (reduced) in the presence of small (large) moist symmetric stability.

An ingredients-based, time- and scale-dependent forecast strategy for anticipating cold season mesoscale band formation within eastern U.S. cyclones is presented. This strategy draws on emerging conceptual models of mesoscale band development, advances in numerical weather prediction, and modern observational tools. As previous research has shown, mesoscale band development is associated with frontogenesis in the presence of weak moist symmetric stability and sufficient moisture. These three parameters—frontogenesis, weak moist symmetric stability, and moisture—are used as the ingredients for identifying mesoscale band development in this strategy. At forecast projections beyond 2 days, the strategy assesses whether cyclogenesis is expected. Within 2 days of the event, the strategy places the band ingredients in the context of the broader synoptic flow, with attention to where deformation zones are present, to assess whether banding is possible. Within 1 day of the event, the strategy focuses on assessment of the ingredients to outline when and where band formation is favored. Plan-view and cross-sectional analyses of gridded model fields in conjunction with high-resolution model guidance are used to assess the likelihood of banding and to outline the threat area. Within 12 h, short-range forecasts of the band ingredients are evaluated in concert with observations to make specific band predictions. Particular emphasis is placed on the evolution of the frontogenetic forcing and moist symmetric stability. During the event, trends in observations and short-range model forecasts are used to anticipate the movement, intensity, and dissipation of the band. The benefits and practical challenges associated with the proposed strategy are illustrated through its operational application to the 25 December 2002 northeast U.S. snowstorm, during which intense mesoscale snowband formation occurred. Forecast products from this event demonstrate how the forecast strategy can lead to heightened situational awareness, in this case resulting in accurate band forecasts. This application shows that accurate operational forecasts of mesoscale bands can be made based on our current conceptual understanding, observational tools, and modeling capabilities.

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