Monthly lightning trends over Florida 1989-2004

Monthly National Lightning Detection Network (NLDN) cloud to ground lightning data over Florida from 1989 to 2004 reveals interesting trends. As expected, lightning totals increase greatly during June and taper off during September. The 16 year average for warm season months peaks in July (291,245 flashes). Considerable variability exists with June, July, and August monthly lightning totals varying by 200,000 flashes from year to year. During 2004, the annual total (1,503,373 flashes) was 60% higher than the 16 year average. June 2004 had the greatest number of lightning flashes (529,981). June lightning totals were greatly affected by 2004 counts that were over twice the 16 year average. Although direct causes were difficult to attribute over monthly time scales, during June 2004 the 300 hPa relative humidity (RH) was 10% lower than the 16 year average and the 600 and 500 hPa RH were about 5% higher than the June average. The lowest annual total, about half the average, occurred in 1991 and the fewest flashes (102) occurred during December 1990. These totals do not account for system outages and system efficiency. Florida lightning deaths and injuries have decreased over the 16 year period even though annual cloud to ground lightning flashes appears to have increased. Three warm season lightning peak patterns emerged: early occurring in June (4 years), mid peak in July (7 years) and a late peak in August (5 years). When the warm season lightning peaks, either the 200 or 100 hPa temperature responds inversely and the other temperature peaks with the lightning or remains near zero. Other atmospheric variables show relationships to lightning maxima and minima and may be useful for seasonal predictions.