The Historic 2 April 2017 Louisiana Tornado Outbreak

Abstract

On 2 April 2017 Louisiana saw one of its largest tornado outbreaks since 1950. The day saw a total of 21 tornadoes, six of which were classified as significant (EF2+). This extreme event resulted in an estimated 4.2 million dollars in damage and two fatalities. A climatology of Louisiana individual tornado days dating back to 1950 ranked this event second for total number of tornadoes (21) in a day and second for number of significant (EF2+) tornadoes (6) in a day. To assess the overall impact of this outbreak, the Destruction Potential Index (DPI) was used to compare both the overall number and strength of tornadoes to previous events. The 2 April 2017 event had the highest DPI for the state of Louisiana since 1950. Comparisons made to tornado days in nearby states in the region also highlight the significance of this event. The synoptic conditions of 2 April 2017 were compared to a 25-member synoptic scale composite of past Louisiana tornado days with six or more tornadoes. The composite highlighted anomalies in synoptic ingredients that contribute to tornado outbreak environments. Most notably, the synoptic structure consisted of a more meridional flow pattern, which allowed for stronger moisture transport, low level shear, deep layer shear, and increased thermal advection. This produced an optimal mesoscale environment with high instability and storm-relative environmental helicity. The meteorological significance of this event with respect to Louisiana stems from the uncommon combination of a high shear/high CAPE near-storm environment in a southern tornado outbreak. The high shear/high CAPE environment largely responsible for the 2 April 2017 Louisiana tornado outbreak is more commonly observed in Great Plains tornado outbreaks.