Evaluation of Radar Reflectivity Structures during Six High-Impact Midlatitude Wintertime Cyclone Simulations

A “nor’easter” is a high impact, mid-latitude, wintertime cyclone, occurring in the economically significant and highly populated northeastern United States with the potential for both severe weather-related hazards and economic disruption. Between 1980 and 2011, ten strong December nor’easters produced $29.3 billion in damages. Despite the advances in both computational power and model development during this same period, numerical weather prediction models still experience difficulties accurately simulating the complex internal dynamics, localized banding, and interplay with the background environment inherent with a nor’easter. This examination investigates the capability of the Weather Research and Forecasting model (WRF) to accurate reproduce 3D radar reflectivity structures during six major nor’easter cases of the last decade as measured by their associated northeast snowfall impact scale (NESIS) value. The authors validate WRF-simulated reflectivity structures via direct comparison to Multi-Radar Multi-Sensor system (MRMS) products and the application of contoured frequency with altitude diagrams (CFADs). Study results show WRF-simulated reflectivity values tended toward higher values than MRMS, particularly at levels above 500 hPa. The intensity and duration of synoptic snowfall banding is also exaggerated in the WRF simulations. In addition, new radar – reflectivity-based algorithm was developed to objectively identify the warm, cool, and cold sectors of a nor’easter independently of surface observations, which has the potential to simplify the analysis of mid-latitude weather systems and aide forecasters. Preliminary results indicate the algorithm-based cyclone sector identification performs best with mature mid-latitude cyclones, but further refinement and validation against surface observations are needed.