A Comparison of Precipitation Objects in Midwest Cyclones during IMPACTS

The Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) is a field campaign operated by NASA from 2020-2023 to investigate the structure and evolution of mesoscale snowbands through the use of both airborne and ground-based instrumentation. While a climatology and conceptual model of banded events in the Northeast U.S. has been developed by Ganetis et al. (2018), the broader spectrum of precipitation structures do not all fit the rigid categories of primary or multibands, as defined in previous literature. Some multibands last several hours as discrete, convective-like features, while others may be transient, weaker-reflectivity structures that rapidly grow and dissipate, or merge with and split from each other.

This talk will address the NEXRAD-identified precipitation structure differences between three IMPACTS cyclones, featuring transient structures on 17 February 2022, poorly defined structures on 14-15 February 2023, and persistent, distinct objects on 16 February 2023. For the first two cases, the high-altitude ER-2 and the in-situ P-3 aircraft flew coordinated legs, while the P-3 flew alone for the last case. To provide environmental context, WRF version 4.4 was configured and run over the Midwest for the duration of each event down to 2-km grid spacing initialized from ERA-5 reanalysis, GFS analysis, and RAP analysis. The WRF model, rawinsondes, and reanalyses will be used to investigate the role of shear, frontogenetical lift, and instability in generating and maintaining these precipitation features. MRMS reflectivity, the ER-2 downward pointing radars, and the P-3 cloud probes will be used to understand the precipitation and microphysical structures. The goals of this talk are to summarize the precipitation structures in the cases, as well as determine what forcing led to the case differences and the ability of the WRF model to realistically simulate them.

The WRF model captures the general differences between the three events, but the precipitation features are shifted to the south and more amorphous than observed. All cases are located downstream of a mid-level trough, with a nearby region of conditional and slantwise instability above a layer of sloping frontogenesis; however, the frontogenesis and mid-level instability are more pronounced when the structures are more persistent and convective-like. An analysis of dual-frequency ratio and radar-retrieved mean diameters from the ER-2 radars suggests reflectivity enhancement in the vertical where the zone of sloping frontogenesis coincides with temperatures favorable for aggregation, possibly influencing the location of banding. This is consistent with the changes in particle size distributions as the P-3 flew through these regions highlighted by the ER-2 radars. Given the WRF model’s challenges in simulating these events, we hypothesize that microphysical deficiencies (e.g., lack of aggregation parameterization) may be a reason for the weaker bands than observed.