84th AMS Annual Meeting

Monday, 12 January 2004: 4:00 PM
A forecast strategy for anticipating cold season mesoscale band formation within developing extratropical cyclones
Room 605/606
David R. Novak, NOAA/NWS/HPC, Camp Springs, MD; and J. S. Waldstreicher, L. F. Bosart, and D. Keyser
Poster PDF (1.2 MB)
A forecast strategy for anticipating cold season mesoscale band formation is presented. This strategy draws on a history of climatological and case studies in which single band development was found northwest of developing cyclones associated with deformation and frontogenesis as the midlevel circulation developed, in an environment of near-neutral upright or slantwise stability. These results are synthesized into an operational strategy that assesses cyclone development, deformation, frontogenesis, and upright and slantwise stability in a scale- and time-dependent approach.

The strategy draws on the dynamical link between cyclone development, attendant deformation zones, and subsequent frontogenesis location and magnitude to allow forecasters to assess whether a synoptic environment favorable for band formation will be present as far as two to three days in advance. From 48–24 h before the banding event, the strategy emphasizes an assessment of mesoscale forcing and environmental stability, identifying the threat area for banding by the overlap of strong midlevel frontogenesis with weak upright or slantwise stability. Within 12 h of the event, emphasis is placed on the use of short-range mesoscale model guidance to refine the threat area through evaluation of the evolution of the frontogenetical forcing, environmental stability, and the corresponding model vertical velocity. High-resolution mesoscale (< 20 km) model precipitation fields may also be evaluated at this time for the explicit prediction of “bands,” which can serve to bolster confidence in the likelihood of the event.

The strategy will be illustrated through its application to the 25 December 2002 Northeast United States Snowstorm, in which intense mesoscale snowband formation occurred. In particular forecast model data, observations, and National Weather Service forecast products associated with this storm will demonstrate that although the precise location of band formation could not be specified with confidence, a heightened situational awareness allowed forecasters to recognize mesoscale band formation as it was initially developing, leading to a rapid operational response.

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