Environmental Conditions Associated With Observed Snowband Structures Within Northeast Us Winter Storms

Northeast U.S. winter storms commonly exhibit multiple meso-beta-scale (L < 200 km) bands of enhanced radar reflectivity and precipitation. We use radar observations, upper-air soundings, and reanalyses from 108 cases of cool season (October-April) storms from 1996 to 2016 that occurred within the coastal corridor from Delaware to Maine to identify and assess various banding structures and environments. Banding can occur in several configurations among storms, and banding characteristics can differ at different times within the same storm. We classified 6-h storm periods as containing long (>200 km) single bands, single bands co-occurring with sets of mesoscale multibands, multibands only, and radar echoes without any bands using a combination of automated and manual methods. Use of radar reflectivity data at 0.5-dB precision and a variable rather than a fixed threshold showed that the occurrence of long single bands without any mesoscale multibands was rare, occurring in only 5 of 113 6-h periods. The most frequently occurring band configuration (55%) was concurrent single bands and multibands, which usually were present in the northwest quadrant of mature cyclones. Sets of multibands without a nearby single band usually occurred in the northeast quadrant of a cyclone poleward of weak midlevel forcing along a warm front. Overall, mesoscale single and multibands more commonly occurred after the cyclone occluded than in the developing stages. Multibands occurred in a wide range of frontogenesis and moist potential vorticity environments.