It was chilly and overcast across eastern Colorado yesterday. Checking the weather satellite, one saw that the eastern half of our State was cloud covered while the western half basked in sunshine. Yet, no rain was falling beneath those clouds.
The reason for the dryness was evident on the water vapor imagery which demonstrated a lack of moisture across the High Plains. The upslope, produced by high pressure to our north (creating clockwise winds) and low pressure to our south (producing counterclockwise winds), pushed the relatively dry air toward the Front Range. As it rose, the air cooled and the moisture condensed as a cloud layer; while fog and drizzle likely developed in the upper foothills and lower mountains, the Piedmont and High Plains remained dry.
On the satellite image, one could see a dramatic demarcation where the Front Range blocked any further westward advance of the upslope-induced clouds. While the upslope flow dropped afternoon temperatures into the fifties (F) across Metro Denver, the humidity in that air was too low to trigger precipitation. Given the fact that the cloud deck was at least 2000 feet above the city, one can assume that the dew point was in the forties, at most. By evening, as the upslope began to dissipate, clearing developed to our west and the loss of cloud cover overnight enhanced radiative cooling, dropping our morning low into the forties. As winds shift from the northwest (downsloping across the urban corridor), warm and sunny conditions will prevail today.
