The days of late summer are here in the Front Range of Colorado and along with them come the first hints of Fall. Stronger cold fronts, which are normally absent during June and July start sweeping southward across Colorado during mid to late August bringing with them cooler temperatures and relief for the sweltering Eastern Plains. The effects of these ‘cold air’ intrusions are at first short-lived. Often they are accompanied by showers and thunderstorms and, after the cold air settles in, low-clouds, fog and drizzle. Warm temperatures are quick to return, even during September, leaving plenty of days to hike and enjoy the outdoors. In the mountains, snow normally falls by early September, but even there warm days and strong sun result in quick melting.
Over the next week, the Front Range will feel the effects of two cold fronts. The stronger one has already passed through the region and forcing from a strong upper level jet streak combined with moist post frontal upslope flow will result in wide spread precipitation over northeastern Colorado, a fairly significant precipitation event for some areas in the Plains tonight into Wednesday morning. Snow will fall in the mountains, especially above 10500 feet, but accumulations should be light.
500mb heights will rise over the area Thursday and Friday resulting in a return to more seasonable temperatures and drier conditions. The next cold front will arrive Saturday afternoon and evening. This looks drier although a few isolated thunderstorms will be possible, and the associated upper level trough will be a quick-mover. By early next week a warm ridge of high pressure will build across the Great Basin into Colorado. As the axis of this ridge slowly shifts to the east, monsoonal moisture will begin to return on southwesterly winds, bringing the return of much needed and appreciated afternoon and evening precipitation.
Notice the smoke? Upper level winds will continue to advect smoke into Colorado over the next several days. By Monday, as these winds back to to the southwest, air quality and visibility will improve.