Wednesday, May 30, 2007

The Palmer Divide

In the western U.S., weather is all about elevation and wind direction. As winds are forced to rise, the air cools and, depending upon regional temperatures, rain or snow develops. Conversely, as winds descend from higher terrain, the air compresses, warms up and dries out.

The Palmer Divide is a ridge of high ground, extending eastward from the Front Range foothills between Denver and Colorado Springs. Averaging 7000-7500 feet in elevation, it separates the watersheds of the South Platte (to the north) and Arkansas (to the south) Rivers. Though of modest height, this ridge often produces a significant difference in the weather of these two cities; yesterday was no exception.

As a cold front pushed across Colorado, tornadic thunderstorms developed on the eastern Plains. Behind the front, northeast winds pushed cool air toward the Front Range; Denver was in the upper 40s by mid afternoon, with cloudy skies and cold rain. As the air was forced up the foothills and onto the Palmer Divide, a mix of rain and snow developed and more storms were generated. Meanwhile, south of the Divide and only 60 miles from Denver, Colorado Springs basked in partly cloudy skies with a temperature of 72. Had the storm tracked to the south, along the Colorado-New Mexico line, upslope would have come from the southeast and the conditions in Denver and Colorado Springs would have been reversed.