The March 2003 snowstorm in southern Colorado

The 17-20 March 2003 snowstorm was a major snowfall and precipitation event for the eastern mountains of Colorado and the nearby plains. This presentation will focus on the effects of the storm for the National Weather Service Pueblo, CO forecast area, which covers most of southeast and south central Colorado. In Pueblo’s forecast area, the heaviest precipitation was on the eastern slopes of the eastern mountains, such as the Rampart Range/Pikes Peak and the Wet Mountains. Ruxton Park, on the east slope of Pikes Peak received about 150 mm of precipitation with 1.5 m of snow. Rye, in the Wet Mountains, received 120 mm of precipitation with 1.15 m of snow.

The storm had deep east to northeast upslope flow around a slow moving upper level cut off low. The development and movement of the cutoff low was the result of four identifiable shortwaves which interacted to produce a prolonged period of deep upslope flow. In the southern half of Colorado, ths storm consisted of two phases. The first phase was characterized by deep easterly flow which advected moist low level air onto the eastern plains and eastern mountains. In this phase, the precipitation was convective with lightning in some of the convective elements. “Thundersnow” was reported in several locations with heavy snowfall rates.

The second phase of the event was characterized by deep northeast flow on the northwest side of an elongated cutoff low. Deep northeast flow can result in significant snowfall over portions of the eastern mountains and nearby plains in southern Colorado This phase exhibited many of the features of a “classic” deep northeast upslope snowstorm with heavy precipitation in regions with orographic lift for northeast flow.

Besides providing a brief overview of the synoptic situation, the orographically related precipitation patterns in southern Colorado with deep upslope flow will be discussed. The eastern mountains in southern Colorado are much more “three-dimensional” than the “Front Range” of northern Colorado. Another important orographic feature is the precipitation shadow over Pueblo and most of Colorado Springs. Northerly flow causes downslope off of the Palmer Divide, and much of the two major urban areas in southern Colorado receive light precipitation while surround areas receive substantially more. Other phenomenon such as barrier jets and their influence on precipitation type will be discussed. One forecast problem throughout the event was influence of the barrier jet on snow level.