The Effect of Diurnal Heating on the Movement of Cold Fronts through Eastern Colorado

摘要

A frequently observed phenomenon unique to the Rocky Mountain region is the apparent effect of diurnal heating on the movement of cold fronts southward through the High Plains. Fronts may stall or slow across Montana and Wyoming during greatest surface heating, with a marked acceleration southward after sunset. Because of this, cold frontal passages seem to occur significantly more often during the nighttime hours in eastern Colorado, especially during the warm season. The propensity toward nighttime frontal passages has been recognized among forecasters, and is considered a general rule of thumb. Whether or not this generalization is founded in fact will be confirmed through statistical means and illustrated by case study. For this purpose, the cold frontal passage of October 20-21, 1981 will be examined briefly. Later it will be shown that for all identifiable cold frontal passages at Denver since 1960, more than two-thirds (69 percent) occurred between the hours of 6 p.m. and 6 a.m.