The relationship between radar reflectivity and lightning activity at initial stages of convective storms

Radar and lightning data sets were collected during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) stationed on the High Plains. This study documents the results of data analysis of 14 storms, 2 with no lightning detected, for which data were collected as part of this study. Previous studies are typically limited in terms of the number of storms studied, or by the lightning data collection systems used. It was found that in all 12 storms with lightning, the initial activity was intracloud lightning. In order for lightning to occur, radar echoes of at least 40 dBZ had to exist at altitudes greater than 7 km MSL. Storms that produced only intracloud lightning differed from those that went on to produce cloud-to-ground strikes in that there were differences in the altitude lightning originated at, and the reflectivity it occurred in. Thunderstorms that displayed positive cloud-to-ground strikes could be distinguished between those with negative cloud-to-ground strikes by the reflectivities present at the time of the initial intracloud strike, and by the time between the first 25 dBZ echo and first intracloud strike. The one case in which a storm switched from negative to positive polarity, differed from a regular negative cloud-to-ground lightning storm in that the initial intracloud strike originated at an altitude less than 8 km. These results show that a combined knowledge of storm intensity and the initial lighting activity may enable lightning forecasts, and aid to improve thunderstorm forecasts.