The 8 May 2009 Superderecho: Analysis of a Real-Time Explicit Convective Forecast

Herein, an analysis of a 3-km explicit convective simulation of an unusually intense bow echo and associated mesoscale vortex that were responsible for producing an extensive swath of high winds across Kansas, southern Missouri, and southern Illinois on 8 May 2009 is presented. The simulation was able to reproduce many of the key attributes of the observed system, including an intense [similar to 100 kt (51.4 m s(-1)) at 850 hPa], 10-km-deep, 100-km-wide warm-core mesovortex and associated surface mesolow associated with a tropical storm-like reflectivity eye. A detailed analysis suggests that the simulated convection develops north of a weak east-west lower-tropospheric baroclinic zone, at the nose of an intensifying low-level jet. The system organizes into a north-south-oriented bow echo as it moves eastward along the preexisting baroclinic zone in an environment of large convective available potential energy (CAPE) and strong tropospheric vertical wind shear. Once the system moves east of the low-level jet and into an environment of weaker CAPE and weaker vertical wind shear, it begins an occlusion-like phase, producing a pronounced comma-shaped reflectivity echo with an intense warm-core mesovortex at the head of the comma. During this phase, a deep strip of cyclonic vertical vorticity located on the backside of the bow echo consolidates into a single vortex core. A notable weakening of the low-level convectively generated cold pool also occurs during this phase, perhaps drawing parallels to theories of tropical cyclogenesis wherein cold convective downdrafts must be substantially mitigated for subsequent system intensification.