Fire managers use the National Fire Danger Rating System to predict the fire danger, or the chance of a wildfire occurring, in a particular region. The system bases its predictions on fuel conditions, latest local weather conditions, and topography. Using advanced computer programs, fire managers calculate four indexes, or indicators, of the fire danger.

People are most familiar with one of these indexes in particular, the Burning Index (BI), which is the one that appears in USDA Forest Service signs warning the public of the risks of a wildfire on a scale of "Low" to "Extreme." Based on the particular fuels of the region, the Georgia Forestry Commission, for example, warns the public of the risk of wildfires using a fuel-dependent BI, which gives a reasonable idea of the flame length in feet at the head of the fire. The flame length is estimated by dividing...