Abstract

Case studies of heavy snowstorms at Denver and Colorado Springs, Colorado, indicate that they occur under different meteorological conditions. The authors examine the hypothesis that there are in fact fundamental differences between the synoptic evolution of events in these two storm types by compositing a total of 28 cases, 17 (11) of which are defined as heavy snowstorms (at least 20 cm of snowfall) at Denver (Colorado Springs). These composited fields were constructed using data at three times in the history of each case. Results show distinct differences in the composited synoptic evolution of the two groups. At low levels the Denver composite shows low static stabilities, warm advection, and high values of potential temperature in the lee of the Rockies. The Colorado Springs composite, on the other hand, shows cold, stable air and cold advection in the lee. At upper levels an eastward-progressing short-wave trough is found at different longitudes in the two composites.

The implied interaction between lower and upper levels of the two composites is also very different. For the Denver composite, the trajectory of the upper-level trough brings it close to the area of low static stability and high surface potential temperature at low levels. This implies strong interaction between the upper-level system and the warm unstable air at low levels and dramatic cyclogenesis east of the Rocky Mountains, typically in southeast Colorado. In contrast, the upper short-wave trough in the Colorado Springs composite is farther north, and a layer of cool stable air is found on the High Plains of Colorado. Not surprisingly, surface cyclogenesis is notably weaker in this composite. These conclusions, substantiated by inspection of the individual cases, have obvious implications for predicting the location of heavy snow along the Front Range of Colorado.

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