Case Study 012"Gravity
Waves"
27 March 1994
Case Summary provided by Dr. Steve Koch, NCSU
This case spans the tornadic outbreak Palm Sunday (27 March 1994) in Alabama. Gravity waves were triggered with deep convection that developed in northeastern Texas. The waves modulated mesolows that developed along a cold front and acted to force the severe convection in Alabama.
Deep convection developed in hightly unbalanced flow in northeastern Texas. These storms triggererd a train of large-amplitude gravity waves, which were maintained by both Wave-CISK and ducting processes in their northeastward movement along and to the rear of the cold front. The waves strongly modulated the frontal mesolows, which were key players in the destabilization and forcing of severe convection in Alabama. Further analysis by Dr. Koch and others has shown that the Texas convection actually generated a mesoscale jetlet that propagated toward Alabama and created inertial instability ahead of the mesolow, and that the vertical circulation associated with this instability was the most important factor in the outbreak of supercell convection. The gravity waves were part of the same geostrophic adjustment process that generated the unbalanced jetlet.
This event was one of the Significant Weather Events of 1994 and resulted in 20 deaths, 320 injuries, and $107 million in damages.