Metro Denver sits in the southwestern corner of a broad, topographic wedge that is bordered by the Front Range, to the west, and the highlands of the Palmer Divide ridge, to the south and southeast. Drained by the South Platte River and its tributaries, this wedge slopes gradually downward to the northeast.
Winds that blow into Denver from the West, South or Southeast descend from higher terrain; since air compresses, warms up and dries out as it descends, the bordering high country keeps the Metro Area dry and sunny much of the time. Then again, March is the snowiest month in Denver as Pacific storms track across the Southwestern States, pulling in moisture from the High Plains and forcing it to rise as it nears the Rockies; rising air cools and expands, triggering precipitation. For Metro Denver to receive significant snowfall, the storm must create a wind field that pulls moisture in from the northeast; storms that produce this scenario generally track along the Colorado-New Mexico line.
Yesterday, as I drove into Colorado, a Pacific storm had pulled out of southern California and was moving across Arizona and New Mexico, producing heavy snows in the southwestern mountains. Ahead of this system, southeast winds were blowing across the High Plains and, by the time I reached Flagler, Colorado, a dense, icy fog had developed; this fog persisted through Limon and onto the south-facing slopes of the Palmer Divide. Once again, the moist flow was rising from lower terrain in southern Colorado and, as it reached its dew point, the dense fog developed. As I descended northward from the summit of the Divide, the fog dissipated and only high clouds obscured the sun.
Though the National Weather Service had predicted heavy snow for Denver, we ended up with only two inches. The heavy snow fell in the southern mountains (San Juans and Sangre de Cristos) and across the south side of the Palmer Divide. The storm had tracked across central New Mexico and a potent upslope flow never developed in Denver. Having lived in the area for 25 years, I have noticed that national forecasters often forget to consider the effects of the Palmer Divide when making their predictions!
