Characteristics of microbursts in central Arizona

Summertime thunderstorms in central Arizona associated with the North American Monsoon often become severe and are known to frequently produce damaging microbursts. Occurring in a rapidly growing metropolitan region, these costly and hazardous phenomena pose a critical challenge to forecasters and are of extreme concern to local power industries and airport operations.

In order to identify the spatial and temporal characteristics, evolution, and intensity of microbursts in central Arizona, data was utilized from a comprehensive radar network put in place to observe the 2008 convective season in the greater Phoenix area. An S-Band WSR-88D and C-Band TDWR were operational throughout the study, offering multiple views of the same storms. Using this new information, microbursts in Central Arizona can be compared to previously documented microbursts from other regions, and evaluated in light of the current theoretical understanding of downbursts.

Microbursts in central Arizona observed during this study were all classifiable as either wet or high-reflectivity microbursts. They occurred most frequently between 5 and 9 PM MST (well after the time of maximum solar heating), and were associated with maximum low-level outflow velocity values either meeting or possibly exceeding those values previously documented. Further, they were observed to occur over scales ranging from 2 to over 20 km in diameter, and minutes to almost an hour in duration. Downbursts evolved in both individual and line microburst formations and exhibited characteristics closely matching, and thus supporting, the currently accepted conceptual models presented in the literature.