Analysis of atmospheric conditions associated with the Embry-Riddle tornado of Christmas Day 2006

During the early afternoon of 25 December 2006, a tornado with estimated F-2 intensity struck the campus of Embry-Riddle Aeronautical University (ERAU), causing approximately $50 million of damage to the university's training aircraft and buildings before moving eastward and significantly damaging an apartment complex about 2 miles away. Fortunately, due to the holiday, the campus was empty and there were no casualties. The tornado, which initially touched down on the eastern edge of the aircraft parking ramp at the Daytona Beach International Airport, was produced from a thunderstorm that had a history of severe-storm and tornadic damage from DeLand, Florida, which is about 25 miles from the Daytona Beach Airport and ERAU campus. The parent thunderstorm was part of a squall line that formed ahead of a strong cold front associated with a vigorous extratropical low and upper-level trough that moved through the southeastern U.S. from 24-26 December. The analysis of this case begins with the synoptic-scale conditions observed during the 12 hours preceding the tornado touchdown. We examine vertical soundings taken in the warm sector ahead of the cold front and compare the thermodynamic and wind profiles to climatological composites for cold-season severe-storm events on the Florida peninsula. As a means of examining the pre-storm environment in the hours immediately before the squall line moved through the Daytona Beach area, we utilize hourly analyses from the Rapid Update Cycle (RUC) model, along with storm-relative velocity and composite reflectivity radar data from the WSR-88D at Melbourne, Florida. Analysis of the local conditions is accomplished using a combination of the radar and Low-Level Wind Shear Alert System (LLWAS) data for the Daytona Beach International Airport. The LLWAS data includes a total of 30 minutes of wind speed and direction information with 10-second resolution from all 9 remote stations, centered on the estimated touchdown time of the tornado on the ERAU campus. Additional analysis of the conditions associated with the tornado is accomplished through examination of the parking diagram for the 65 training aircraft operated by the university and comparing the aircraft tail number positions with damage photographs taken in the days immediately following the event to determine the damage trajectories from initial touchdown. Finally, an intriguing piece of cockpit data recovered from one of the damaged aircraft suggests that the tornadic winds were approximately 120 kt and associated with a 70-mb pressure drop, consistent with the F-2 damage recorded by the National Weather Service survey team.