Abstract

Mountain thunderstorms often originate in preferred regions of the topography, as shown qualitatively by pilot reports and more quantitatively by meteorological radar, satellite, and lightning detector studies. To further investigate the phenomenon of mountain thunderstorm initiation, we used time sequences of GOES imagery to locate storms and to trace them back to their points of origin. Using three summers of data from days which started out clear, we backtracked over 600 storms in the mountains of Colorado and northern New Mexico. We plotted the origin points on a terrain map and drew contours of initiation frequency to identify regions with a high likelihood of producing thunderstorms. We found that initiation sites tended to cluster into identifiable geographical locations or “genesis zones”, consistent with findings based on the other data sources. When cloud propagation effects were taken into account, the locations of these genesis zones were also consistent with the locations of clustering regions found in the other studies. In addition to regions where thunderstorm initiations tended to cluster, there were regions that they tended to avoid, including such broad mountain basins as South Park and the San Luis Valley, and such wide river valleys as the Gunnison and Colorado.

Besides finding preferred locations for storm initiation, we were also able to stratify the data by ridgetop wind direction. Many of the genesis zones were active only under certain wind regimes. For example, in the southern Sangre de Cristo Mountains, storm initiations tended to occur to the lee of the range under southwesterly, northwesterly, and southeasterly flow at ridgetops. Knowledge of the prevailing flow directions under which genesis zones were active allowed us to determine mechanisms which contributed to storm initiation.

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