Science-to-Service Methods During a Violent Tornado in Southeast Iowa During the Historic 31 March-01 April 2023 Tornado Outbreak

The United States’ third largest tornado outbreak on record since 1950 occurred on 31 March - 01 April 2023 with 147 tornadoes across 11 states, including a large portion of eastern Iowa and Illinois. Within the NWS Quad Cities, IA/IL county warning area (CWA) there were 29 tornadoes, with a staggering 15 that were rated EF2+, which were the most strong tornadoes in the CWA from a single event on record. This included the strongest tornado of the national outbreak, an EF4 near Keota, IA, having peak estimated winds up to 170 mph, a 20 mile path length, and a maximum width of 700 yards. It was the first EF4 in the CWA since 1995, which underscores the rarity of violent tornadoes in this portion of the country. Despite that, there were no fatalities and only 11 injuries in the CWA.

Significant severe weather potential had been consistently highlighted and honed in space and time in NWS outlooks six days in advance to impact-based warnings the day of. On the morning of 31 March, the NWS Storm Prediction Center issued a High Risk convective outlook – the first to include the NWS Quad Cities CWA in nine years. Two markedly contrasting convective modes comprised this event in the CWA, each capable of strong tornadoes. The evolution was a period of long track supercells transitioning to a mature tornadic QLCS. The dramatic change in storm morphology led to a rapid increase in areal coverage of severe storms, which required different radar analysis techniques and made for challenging convective warning decisions. Translating that into tactical messaging for decision-making core partners was paramount, and NWS Quad Cities held “live” tactical webinars throughout the entirety of the event providing timely and actionable information.

The parent supercell of the Keota, IA area EF4 tornado had multiple unique meteorological aspects that were translated into Tornado Warnings and other external NWS messaging. This included optimal near-storm environment and supercell structure and motion to maximize streamwise vorticity for a longer duration than other storms in the region. This supercell also had a remarkable 45-minute average tornadic debris signature (TDS) height of 21,300 ft. These were translated into impact-based decision support services (IDSS), in particular actionable messaging, especially during these tactical webinars.

This analysis will explore the environmental to storm scale setup that contributed to the tornado outbreak and the character of its evolution, in particular the violent tornadic supercell near Keota, IA, and how meteorological analysis was translated into effective tactical messaging that likely contributed to saving lives.