A Summertime Tornado Outbreak in Colorado: Mesoscale Environment and Structural Features

Abstract

On 14 August 1977, there was a mini-outbreak of three tornadoes about 40 km cut of Denver, Colorado. There were no significant synoptic-scale disturbances affecting Colorado on that day. Mesoscale analysis is used to establish several smaller scale systems that influenced storm development. The most notable feature of the mesoscale band of parent thunderstorms was the active growth along their northwest flank, in spite of cell movement toward the east. On the convective scale, the situation can be described as discrete propagation of multi-cell storms by new cell development on the left rear flank. Two of the three tornadoes were documented photographically, and post-analysis shows that they were of large size and long duration, but slow moving. Structural features of the largest tornado are analyzed in different portions of the life cycle, and compared with other cases in the literature. This tornado moved on a track curving toward the north-northwest, remaining at least 5?10 km distant from any significant precipitation. A dust band believed to represent an inflow jet was observed, which was in a different quadrant from similar features in other cases. Aspects of the tornadoes which could cause public confusion are noted, such as the disproportionately short condensation funnel from high-based cumulus clouds.