Observed hazards to aircraft in deep summertime convective clouds from 4-7 km

Data from flights by the South Dakota School of Mines and Technology’s North American T-28 storm-penetrating aircraft during nine different research projects conducted between 1991 and 2003 are analyzed. These flights, usually flown during the summer months in the central and high plains in the United States, targeted regions of convective storms containing vigorous updrafts, downdrafts, and precipitation, including hail. Observations indicate that three of the most hazardous components of flying in summertime deep convective clouds are aircraft icing, turbulence from strong vertical wind gradients, and hail. There is also a smaller, but still important, threat from lightning. Statistics of the observations show that at any given time there is approximately a 10% probability of encountering severe icing conditions, approximately a 0.1% probability of encountering extreme turbulence, and approximately a 0.2% probability of encountering hail with mean diameter 2.5 cm or greater within convective clouds in the 4-7 km mean sea level altitude range. The purpose of this study is to analyze the convective environments under which these hazards occur in order to provide reference and/or guidance for conditions that might be encountered within summertime convective clouds by aircraft.