Examining the role of mesoscale features in the structure and evolution of precipitation regions in northeast winter storms

Cold-season frozen precipitation in the northeastern United States is manifest in a variety of spatial patterns evident on radar imagery. Although forecasters can predict likely areas of precipitation, considerable difficulty remains in properly identifying mesoscale precipitation signatures within the main precipitation shield. As viewed on a radar image, precipitation can appear splotchy, relatively uniform, banded, or a combination of all three. Being able to forecast mesoscale precipitation characteristics is vital in adding value to a forecast by enhancing the mesoscale prediction of snowfall amount and variability. The purpose of this presentation is to examine the role of mesoscale forcing and instabilities in the structure and evolution of precipitation regions in Northeast winter storms.

Thirty "heavy snow" events in the Northeast from the past three winters have been selected for analysis. The precipitation in each event is classified as being primarily warm air advection-driven ("overrunning"), primarily differential cyclonic vorticity advection-driven ("wrap-around"), or a blend of the two. High-resolution radar mosaics are used to diagnose the character of the mesoscale precipitation patterns in each of the 30 events. Events with similar mesoscale precipitation patterns are used to create storm-relative flow composites for the three event classes. Appropriate horizontal maps and cross sections are created for the respective composites to ascertain relationships between mesoscale forcing and instability signatures and the precipitation mode. For example, this presentation will demonstrate connections between frontogenesis, moist gravitational and symmetric instability, and mesoscale bands oriented along the thermal wind. A representative case study from the 2004-2005 winter is included to document the connections between synoptic and mesoscale circulation features and precipitation mode.

Radar imagery exhibiting various precipitation patterns can be found at http://www.atmos.albany.edu/student/greenstein/ABQ.