Warm Season Cloud-to-Ground Lightning–Precipitation Relationships in the South-Central United States

This study examines the relationship between cloud-to-ground (CG) lightning and surface precipitation using observations from six regions (each on the order of 10 000 km2), April through October (1989–93), in the southcentral United States. The relationship is evaluated using two different methods. First, regression equations are fit to the data, initially for only the CG lightning flash density and precipitation, and then with additional atmospheric and lightning parameters. Second, days are categorized according to differences in the precipitationto-CG lightning ratio; the same additional parameters are then examined for differences occurring within each category. Results show that the relationship between CG lightning and surface precipitation is highly variable; r2 coefficients range from 0.121 in Baton Rouge to 0.601 in Dallas. A measure of the positive CG lightning flash density is the best addition to the model, statistically significant in all regions. When days are categorized, the percentage of lightning that is positive shows the most significant differences between categories, ranging from ,4% on days with a ‘‘low’’ precipitation-to-CG lightning ratio, to 12%–36% on days with a ‘‘high’’ ratio. Other lightning parameters give less significant results; however, three atmospheric parameters (CAPE, lifted index, and Showalter index) do show a significant trend suggesting that there is much less instability in the atmosphere on ‘‘high’’ ratio days than on ‘‘low’’ ratio days.