The storm that dumped heavy snow on Colorado's Front Range, just a few days ago, was the result of a trough (a dip in the jet stream), which allowed cold air to spill southward and triggered a potent zone of low pressure; the latter, which moved from the Great Basin onto the High Plains, produced upslope flow across eastern Colorado and heavy, wet snow for most areas above 5000 feet.
Moving off to the east, where it ignited thunderstorms and heavy rains, the trough was replaced by an atmospheric ridge, a northward bowing of the jet stream. In contrast to the trough, the ridge permits warm air to push up from the Southwest; as it crosses the Rockies, this air is forced to sink, further compressing, heating and drying its mass. As a consequence, the recent snow has essentially disappeared from elevations below 6000 feet and, with sunny, warm conditions expected this week, the snowpack in the foothills and mountains is sure to follow.
Tributaries of the South Platte are already swollen with meltwater and standing pools cover flat areas of the Piedmont and Valley floor. All of this heat and moisture will boost the growth of foliage, foster the birth of insects and set the stage for summer birds to arrive. Just a typical April sequence along the Colorado Front Range.
