Dense Fog in Animas River Basin, Colorado

Areas of dense fog developed within the Animas River Basin overnight on December 4-5. The KDRO ASOS at the Durango La-Plata County Airport reported over two hours of 1/4-mile visibility due to freezing fog. No reports of injuries, damages, or fatalities were received.

A drying atmosphere was established over western Colorado underneath high pressure ahead of a shortwave trough. In spite of this, a pool of surface moisture remained trapped within southwestern Colorado valleys due to a December 2 storm which dropped several inches of snow over the San Juan Mountains. The low-level environment here remained near-saturated for several days as a result. Reduced visibility from mist and fog was exhibited in the nights prior, but cooler overnight low temperatures led to dense fog development and 1/4-mile visibility overnight from December 4-5.