A Climatology of Cool-Season Precipitation Structures Within the Cyclone Comma Head

Winter storms have a variety of precipitation structures ranging from cells to banded precipitation within the cyclone comma head. Much of the previous research has explored primary snowbands, but there has been little investigation of the broader spectrum of snowband structures that may not fit the past definitions of primary or multibands. The current conceptual model of precipitation bands as described in Houze (2014) also does not account for findings from more recent field campaigns, and does not link this larger spectrum of structures to the various environmental conditions including lifting mechanism, stability, moisture, and shear.

A new algorithm is used in this talk to identify precipitation structures in extratropical cyclones, building on work done by Ganetis et al. (2018). This algorithm divides a larger domain into several smaller boxes and computes the upper sextile reflectivity in each box, to focus on local enhancements of reflectivity. Composite radar over the Northeast U.S. and adjacent coastal waters from 1996-2023 is used for the analysis. The thermodynamic and kinematic environment is also computed in a cyclone-relative frame from ERA-5 reanalysis. Results are also separated by the orientation of the cyclone track.

The distribution of precipitation objects does not appear to be separated into distinct distributions of primary or multibands, as the histograms of area, length, or width resemble an exponential curve. Nevertheless, band-like objects most frequently occur northeast of the cyclone center for storms with a more zonal track, or north-northwest of the cyclone center for storms with a more meridional track. Larger bands are coincident with mid-level frontogenesis and slantwise instability, while upright instability is more common in regions of more amorphous bands. The variability of band shapes will be further highlighted in sub-regions around the comma head and related more directly to local shear, instability, and frontogenesis.