How the Coupling of the Synoptic-Scale Environment and a Mesoscale Baroclinic Boundary Led to the 22 January 2017 Tornado Outbreak in South Georgia
Jeffrey Fournier, NOAA/National Weather Service WFO Tallahassee, Tallahassee, FL
Parks Camp, NOAA-National Weather Service

The 22 January 2017 tornado outbreak was the deadliest in south Georgia in nearly 17 years. From the pre-dawn hours through mid afternoon, two EF-2 and two EF-3 tornadoes struck south Georgia, killing 16 people. The synoptic environment featured many of the ingredients often associated with tornado outbreaks, including unusually strong vertical wind shear in both the

0-1 km and 0-6 km layers, large height and pressure falls ahead of a potent shortwave trough, a warm, moisture-rich boundary layer, and a moderately-unstable airmass. Additionally, a mesoscale baroclinic boundary played an important role in this outbreak by concentrating the most favorable conditions for strong mesocyclones over a relatively small region in south Georgia.

During the afternoon and early evening hours of 21 January, persistent, concentrated convection formed a surface-based cold pool across much of south Georgia. The outflow boundary along the southern flank of this cold pool oscillated back and forth over a 20 NM-wide zone from the night of 21 January through the afternoon of 22 January, as southwest winds of 50 knots at

850 mb battled reinforcing cold pools from new periods of convection. With a synoptic environment already conducive for rotating updrafts, the supercells which produced the strongest and longest-lasting tornadoes benefited from the enhanced vertical and horizontal vorticity within the persistent and well-defined baroclinic zone.†††

There have been several past examples of tornadoes developing in such baroclinic zones, but the importance of routine surface analyses during unfolding severe weather events is often minimized during warning situations. Instead forecastersí attention is typically drawn toward radar data. Although the NWS provided significant lead time in its warnings for these tornadoes, itís possible that forecasters may have communicated an enhanced risk of tornado development for a relatively small geographical region and temporal window if they had more detailed knowledge of evolving surface features.