Environmental analysis and photographic documentation of an intense, left-moving supercell on the Colorado plains

On the afternoon of 15 June 2002, an anomalously intense, anticyclonic supercell affected the Aroya, Colorado area, producing hail up to 5 cm (2 inches) in diameter. This storm is documented and analyzed using multiple platforms, including satellite imagery, radar imagery and field photography. The storm’s evolution and morphology is examined and compared across both remotely sensed and directly observed perspectives – a common theme for observational studies of cyclonic supercells but not for left-movers. We illustrate a persistent and anomalously intense mesoanticyclone in this storm. Observational data and RUC model soundings (Thompson et al. 2003) are used to evaluate the storm’s environment and assess the predictability of its unusual, east-southeastward motion for a left-moving supercell. The effective environment – both in storm-relative and Galilean-invariant frameworks – changed rapidly before storm initiation from one favoring right-moving supercells to one favoring left-movers. We illustrate the adjustments in vertical shear and buoyancy related to the presence of postfrontal and outflow air left behind by convection from earlier the same afternoon. In addition, ground photography is inverted into mirror image and compared to similar imagery of cyclonic supercells, for utility in both conceptual relation and in visual recognition by storm spotters.