Using MRMS Rotational Tracks for Northeastern US Tornado Warning Guidance

Between January 2017 and July 2023, 371 tornadic events occurred within New England, New York, New Jersey, and Pennsylvania. Forecasters at the National Weather Service (NWS) Albany Weather Forecast Office have traditionally used the V-R Shear relationship between gate-to-gate shear and rotational velocity as a part of the tornado warning process. Assessing rotation strength through this method can be time consuming, as the warning meteorologist needs to look at either a vertical cross-section or multiple plan view images at different radar elevation slices to assess the strength of the mid-level rotation. As a result, more tools and strategies are needed to help meteorologists to quickly evaluate storm-scale rotation.

With its fast temporal updates, Multi-Radar Multi-Sensor (MRMS) rotational tracks can be a useful tool during the tornado warning process. The NWS Radar Application Course (RAC) teaches that both low and mid-level rotation tracks from the MRMS can be useful for a warning meteorologist to examine, as they show the maximum azimuthal shear within different layers. These rotation tracks based on data from more than one radar also have the benefit of mitigating some of the issues with beam blockage and beam widening that occur when using data from just a single radar site.

This study examines both low level (0-2 km AGL) and mid level (3-6 km AGL) MRMS rotation tracks for 320 Northeastern United States tornadic events between 2017 and 2023. Twenty-four null cases were also examined for when tornado warnings were issued and no tornadoes were reported. The results showed similar values to the warning threshold recommendations from RAC (0.015 s-1 for level level rotation and 0.010 s-1 for mid-level rotation) and found slightly higher values for the tornadic events vs. the null cases, mainly for the stronger tornadic events (EF2+). These results show that MRMS rotational tracks could be a useful supplement to other warning strategies during the tornado warning process.