Initiation and Evolution of Summertime Storms in Central Arizona

High resolution radar reflectivity data coupled with digital elevation terrain information is examined to determine the important meteorological and geographical attributes that lead to preferred areas for convective initiation and propagation in the southwestern United States. Previous studies show terrain influences the climatological diurnal precipitation cycle in central Arizona during the summertime, however, a study examining the role of terrain and associated synoptic and mesoscale conditions on preferred storm initiation locations and storm evolution does not exist. To this end WSR-88D 1-km resolution radar reflectivity mosaics, digital elevation data, and surface and upper-air data is used to examine important meteorological traits that lead to preferred areas for storm occurrence over central Arizona during July and August 1999. For each day, regions of convective initiation and storm evolution patterns are identified using diurnal relative frequencies of mosaiked radar reflectivity. Associated synoptic and mesoscale conditions, such as surface moisture, surface and upper air wind profiles, and stability, are examined to possibly elucidate the mechanisms behind different storm initiation and evolution regimes.

While the initial results show that convection commonly initiates near mountain peaks or ridges, such as the White Mountains, Central Mongollon Rim and the San Francisco Mountains, the timing and orientation varies significantly. Like the initiation locations, a significant variance in the storm evolution is also observed. For example, on some days, storms form only along the Mongollon Rim and/or Southeast Highlands, while on other days, mountain-initiated storms propagate off the mountains initiating storms in the Phoenix Metroplex and the lower Sonoran Desert. Since common storm initiation locations exist in central Arizona, an analysis of associated wind and moisture regimes has strong potential for providing useful guidance for forecasting where storms will occur on a given day.