Leaving the Arctic

Yesterday morning, we left Missouri for our Littleton, Colorado, farm; the temperature at dawn was 5 degrees F.  Heading west on Interstate 70, we encountered a frigid, snow covered landscape all the way to eastern Colorado.

Enroute, the air temperature gradually climbed to the mid 20s on the High Plains but plunged a bit on the south side of the Palmer Divide, where a southerly upslope produced an icy fog.  Once we crossed the divide, however, the skies began to clear and the temperature rose into the upper 30s, the warmest weather that we had encountered in weeks.  As the latest winter storm pulls off to the east, bringing more snow and ice to the southern U.S. and the Northeastern States, a southwesterly wind will  descend along the Front Range, producing afternoon highs from the upper 40s to the upper 50s; it will feel like the Tropics after enduring Arctic air for most of the season.

While Denver is renowned for its proximity to ski areas and may receive snowfall from September to May, it and other Front Range cities enjoy a relatively mild winter compared to areas in the Upper Midwest; for example, the average high temperature in late January is about 40 degrees in Denver, compared to the upper 20s in Chicago.  Though the high elevation and thin atmosphere increase solar heating, the primary reason for both the frequent snow and the mild winter interludes is the city's location at the base of the Front Range; upsloping air from the Plains (especially from the northeast) produces snowfall (if sufficient moisture is present in the atmosphere) while downsloping air from the mountains brings mild conditions and sunny skies.  As the air sinks from mountain elevations, it dries out and heats up; such chinook winds rapidly melt the snow on the Piedmont and can bring May-like warmth in the midst of winter.