The values for GFD shown on the map in Fig. 3 are longterm average GFDs. Since GFD can vary considerably from
these average values on an annual basis, for transmission line designs the low end of the range for GFD values is assumed to be 50 percent of the average value for the area. The high end of the range is assumed to be 200 percent of the average value.For example, for Orlando, Florida, the average GFD value from Fig. 1 is 18 strikes per square kilometer per year. The GFD range would be 9 to 36 strikes per square kilometer per year.