Regional Biases in Tornado Detection: Cross-Validation of SPC Reports and MRMS Azimuthal Shear

Abstract

This study examines the spatial correlation between low-level rotation fields from the Multi-Radar Multi-Sensor (MRMS) system and tornado reports from the Storm Prediction Center (SPC) between 2021 and 2023. Tornadoes were analyzed by overlaying reported paths onto MRMS RotationTrack60min fields, which capture maximum low-level azimuthal shear over a rolling one-hour window. Two spatial search methods were used: a radial search centered on each tornado’s reported start point and an interpolated path-based search along the full track. Results show that MRMS-detected rotation signatures were found within 5 kilometers of approximately 95% of tornado reports using the radial method, with marginal improvement from path interpolation. Regional differences were evident; tornadoes in Tornado Alley exhibited stronger rotation and higher detection rates than those in Dixie Alley. Tornadoes associated with stronger radar-indicated rotation were also more likely to align with reports, revealing a detection bias toward more intense systems. These findings underscore the strengths and limitations of MRMS azimuthal shear for tornado detection. While MRMS enhances identification of well-organized tornadoes, weaker or short-lived events remain harder to detect. This research contributes to improving tornado climatology and real-time warning systems by cross-validating radar data with observational records. Future work expanding the MRMS archive and incorporating environmental classifications will further refine understanding of tornado detection efficiency.