The relationship between aircraft icing and synoptic-scale weather conditions

More than 2700 aircraft icing pilot reports are compared to analyses of operationally available data for 37 cases of winter weather. Statistical results regarding the number of occurrences of icing reports with airmass origin, location relative to fronts, troughs and low pressure centers, precipitation type, cloud cover, lightning/thunder, fog, radar reflectivity, and synoptic-scale forcing mechanisms are developed. Statistics are created for several combinations of icing severity and type, including a category for some of the worst icing encountered by aircraft (clear or mixed icing of moderate or greater severity), then normalized by the areal extent of the weather features. Results indicate that the locations most conductive to icing conditions were arctic, West Coast, and East Coast air masses; 250-600 km ahead of active and stationary warm fronts; in areas of freezing drizzle, freezing rain, and ice pellets when precipitation was occurring; and in areas with obscured and overcast sky conditions when precipitation was not occurring. Icing conditions were also associated with overrunning conditions and troughs analyzed on upper-air charts. Conditions in some of these locations were conductive to the formation of large supercooled water droplets, which have recently been shown to be related to hazardous icing conditions.