Date of Award

December 2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Atmospheric Sciences

First Advisor

Jake Mulholland

Abstract

Tornadoes are among the costliest and deadliest severe weather events in the United States. Doppler weather radar is one of a meteorologist’s most useful tools for early detection of tornadoes. However, there are several notable areas across the Northern Plains (Minnesota, Montana, North Dakota, and South Dakota) where the National Weather Service’s (NWS) radar coverage exceeds 10,000 feet above radar level, leaving an effective “radar gap” where tornado detection becomes increasingly challenging, if not impossible in some cases. Even within these radar gaps, the NWS is still responsible for issuing Tornado Warnings to fulfill their mission of protecting life and property. To better understand the scope of this problem, this M.S. Thesis examined the climatology of tornadoes across the Northern Plains. This project aimed to better understand the diurnal, monthly, seasonal, and yearly trends of tornadoes across the Northern Plains. Additionally, it examined the frequency of tornadoes occurring within radar gaps across the Northern Plains, in order to better identify where tornado warning decisions become more challenging. Finally, three hypothetical scenarios are considered, focusing on a combination of new radar sites and additional lower-level beam elevations which show some potential improvements to the existing NWS WSR-88D Doppler radar network across the Northern Plains and in surrounding states. Results indicate climatological trends of peak tornado reports across the Northern Plains in the late Spring to early Summer months, with the highest amounts of reports occurring during the mid-afternoon to late evening hours. Results also indicate that since the implementation of the NWS WSR-88D Doppler radar network, roughly 16% of reported tornadoes across the Northern Plains occurred within one of these “radar gap,” with results varying by state. Probability of Detection (POD) and False Alarm Rates (FAR) were also examined for NWS Tornado Warnings across the Northern Plains. While the regional POD has decreased since the radar network’s upgrade to dual-polarization in 2012/13, individual NWS offices show varying results. Finally, the three hypothetical scenarios indicate that the addition of a lower radar beam elevation scan and/or additional radar sites in critical areas would decrease the amount of tornado reports occurring within these “radar gaps.”

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