Variability of Cool Season Precipitation Structures Within the Cyclone Comma Head

The Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) is a field campaign operated by NASA to understand the structure of mesoscale snowbands. While many studies have explored single (primary) bands in the cyclone comma head, few studies have included the broader spectrum of precipitation structures that may not fit the current rigid categories 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. An updated precipitation band climatology around the cyclone would allow one to better understand the environmental conditions that favor the spectrum of precipitation structures within the comma head within the context of lifting mechanism, stability, moisture, and shear.

This talk will highlight two new algorithms developed to identify mesoscale precipitation structures in extratropical cyclones, building on work done by Ganetis et al. (2018). Unlike older approaches that objectively identified structures relative to a single background radar reflectivity threshold for a large region (e.g., Northeast U.S.), these algorithms will focus on objects enhanced locally relative to their background, better capturing the variability of structures across multiple length scales. The first algorithm divides a stitched reflectivity domain into several smaller boxes and computes the upper sextile reflectivity in each box, rather than throughout the whole domain, while the second algorithm uses an updated convective-stratiform method (Yuter and Houze 1996) tuned for winter weather to identify structures separated from the background by the gradient of precipitation intensities. Image processing techniques such as image morphology and watershed segmentation are also utilized to further separate regions of enhanced precipitation into discrete objects. Both algorithms have been applied to cool season extratropical cyclones from 2000-2023, with preliminary results showing prevalent sizes and structures for different stages of cyclone development, to better understand the evolution of structures as a cyclone deepens and matures. These results will be compared against several winter storm cases sampled by the IMPACTS field campaign during the 2020, 2022, and 2023 deployments. The thermodynamic environment will also be computed in a cyclone-relative frame for each case from ERA-5 reanalysis.