CLIMATOLOGY, SYNOPTIC ASSESSMENT, AND THERMODYNAMIC EVALUATION FOR CLOUD-TO-GROUND LIGHTNING IN GEORGIA - A STUDY FOR THE 1996 SUMMER OLYMPICS

A lightning climatology within 50 km of nine outdoor venue locations f or the 1996 Summer Olympics has been produced. Spatial and temporal pa tterns were analyzed for July and August from 1986 through 1993. Unusu ally active and inactive lightning days were isolated, and thermodynam ic variables examined. At the inland sites, no pattern was found in th e spatial distribution of cloud-to-ground lightning; that is, the ligh tning locations were random. At the one coastal site, Savannah, an inl and maximum in ground flash density was observed. Although there was g reat day-to-day variability, there was a diurnal progression of lightn ing with a broad minimum from 0600 to 1400 UTC and a sharp maximum nea r 2200 UTC. Composite synoptic charts were produced for eight selected active days and eight selected inactive days. At the 500-hPa level th e composite dewpoint depression in central Georgia was approximately 8 degrees C less on active days than on inactive days. At the 850-hPa l evel the vector-averaged wind fields on active days revealed weakly an ticyclonic southwesterly flow throughout Georgia. On inactive days, th e vector-averaged winds exhibited a large anticyclone centered in nort hern Georgia. Some correlation was found between cloud-to-ground light ning activity and several of the thermodynamic variables. The most hig hly correlated was a form, of convective available potential energy wi th a correlation coefficient of 0.70. The Showalter stability index an d K index had correlation coefficients of 0.60 and 0.56, respectively. Logistic regression equations were developed to forecast active and i nactive lightning days from thermodynamic variables and persistence. D ays of unusually low lightning activity were more accurately identifie d through logistic regression than days of unusually high lightning ac tivity. To aid in forecasting lightning days, the historical probabili ty of active or inactive lightning days is provided as a function of t he logistic model output.