Observed Characteristics of Mesoscale Snow Bands in the Coastal Northeast U.S.

It has long been recognized that mesoscale precipitation bands within extratropical cyclones can dramatically affect the short-term intensity and total accumulation of winter precipitation. Mesoscale snow bands manifest a variety of horizontal length and time scales ranging from 10s to 100s of km and less than an hour to multiple hours in duration. Some storms exhibit a large single band, some have multiple smaller bands, and other storms have a mixture of both. Band characteristics can vary between different times in the same storm. This portion of a joint observational-modeling study focuses on snow band identification and characterization using radar data.

We examined NWS operational radar data from 70+ snow storms occurring during October through March from 1995-2015 along the northeastern coast of the United States. The study area extends from Delaware to the southern coast of Maine with the main focus on the corridor between New York City and Boston. Radar data from six WSR-88Ds were quality controlled, combined into a regional composites, and analyzed. More than 170 storm days were examined with the longest storm lasting 75 hours. Objective identification of bands is accomplished based in part on detection of relative peaks in radar reflectivity using a variant of a convective stratiform precipitation algorithm and on image morphology techniques. Automated band detection is evaluated using subjective visual analysis. Characteristics of mesoscale snow bands such as horizontal length, intensity, and duration will be obtained to yield information on the properties and variability of mesoscale snow bands across the northeastern United States. This information will be used in turn to inform an associated modeling study.