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Sebastian S. Harkema, Emily B. Berndt, and Christopher J. Schultz


It has been theorized that thundersnow (TSSN) occurs in conjunction with heavy snowfall rates and in geographical regions where heavy-banded snow occurs more frequently. This study aims to objectively and quantitatively identify characteristics associated with TSSN to improve the situational awareness of heavy snowfall and associated hazards. The Geostationary Lightning Mapper (GLM), National Environmental Satellite Data and Information Services (NESDIS) merged Snowfall Rate (mSFR) product, and surface observations were utilized to characterize snowfall accumulation, snow-to-liquid ratio (SLR) values, and radar characteristics of heavy snowfall events from a GLM perspective. When at least 2 in. of snowfall accumulation occurred, areas with TSSN flashes identified by the thundersnow detection algorithm (TDA) were likely to receive, on average, a total of 24.5 cm (9.6 in.) of snowfall. TSSN was more likely to occur in snowfall rates less than 2.54 cm h−1 (1 in. h−1) and be associated with snow-to-liquid ratio (SLR) values between 8:1 and 10:1. It was determined that TSSN flashes observed by GLM occurred in isothermal reflectivity values less than 30 dBZ and average spatial offsets of 131 km between the lightning flash location and the heaviest snowfall rates were observed. GLM flashes in proximity of National Lightning Detection Network cloud-to-ground flashes and tall structures were found to be statistically different (p < 0.05) regarding snowfall rates, SLR values, and various Multi-Radar Multi-Sensor variables compared to other TSSN flashes. It was inferred that tower TSSN flashes, on median, were more likely to initiate within light-to-moderately rimed snowfall. Last, a heavy snowfall event was analyzed to demonstrate the capability of these products in identifying storm characteristics associated with TSSN.

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Sebastian S. Harkema, Christopher J. Schultz, Emily B. Berndt, and Phillip M. Bitzer


This study examines characteristics of lightning in snowfall events (i.e., thundersnow, TSSN) from the perspective of the Geostationary Lightning Mapper (GLM) and the National Environmental Satellite Data and Information Service (NESDIS) merged Snowfall Rate (mSFR) product. A thundersnow detection algorithm (TDA) was derived from the GLM and mSFR that resulted in a probability of detection (POD) of 66.7% when compared to the aviation routine weather report (METAR) reports of TSSN. However, using the TDA an additional 2175 lightning flashes within detected snowfall were identified that were not observed by the METAR reports, indicating that TSSN has been under reported in previous literature. TSSN flashes observed by GLM have mean flash areas, durations, and total optical energy outputs of 754 km2, 402 ms, and 1342 fJ, which are between the 50th and 99th percentile values for all flashes within the GLM field of view. A comparison with data from the National Lightning Detection Network (NLDN) indicated that the NLDN had at least one cloud or ground flash detection in 1709 of the 2214 flashes observed by GLM in snowfall. An average of 5.85 NLDN flashes was assigned to a single GLM flash when the NLDN flash data were constrained by the GLM flash duration and spatial footprint. Statistically significant (p < 0.01) differences in flash area and flash energy were found between flashes that were observed by the NLDN and those that were not. Additionally, when GLM was combined with the NLDN, at least 11.1% of flashes involved a tall human-made object like an antenna or wind turbine.

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