Aircraft Icing Conditions in Northeast Colorado

The in-flight icing environment in northeastern Colorado is described through remote and in situ measurements. Four field efforts in the winters of 1990 through 1994 were conducted in the area, and comprehensive datasets from research aircraft, ground-based multichannel microwave radiometers, and in-flight pilot reports were collected. Many aspects of the icing environment are examined: synoptic and mesoscale weather related to icing conditions, frequency of liquid-bearing clouds and potential icing conditions, microphysical characteristics of the clouds, and icing type and severity. Most clouds with supercooled liquid water sampled during these field projects were associated with cold fronts or cold surges or with widespread cyclonic or anticyclonic circulations that produce upslope cloudiness. The cloud characteristics were typically winter continental, with small droplets and low liquid water contents (both as in situ–measured cloud liquid water content and remotely sensed integrated amounts). Integrated liquid water values from ground-based microwave radiometers were typically low (usually less than 0.1 mm) but were higher over instruments situated nearer to the mountains; little diurnal trend was noted for any site. The aircraft database is described in detail in terms of three icing-critical cloud parameters (liquid water content, droplet size, and temperature). Most icing conditions reported by pilots flying in the area were light to moderate in severity and were rime in type. Comparisons of the data with measurements from other projects and locations are made.