The coupling of large scale weather conditions with local scale weather and fuel conditions was examined for 2551 fires and 1,537,624 lightning strikes for the May through August fire seasons of 1988, 1989, 1992, and 1993. The probability of fire occurrence was best correlated to the moisture of fine fuels, which have an equilibrium drying time of two days. However, in all cases, the number of strikes greatly exceeds the number of forest fires, indicating that ignition is a rare event. Persistent (longer than 2 days) high pressure at the 50 kPa level produced drier fuels and a higher density of strikes than did other 50 kPa conditions. Thus, the highest probability of fire occurs during persistent high pressure systems. The occurrence of lightning during a high pressure weather system has been correlated to an index of atmospheric instability. This indicates persistent high pressure weather systems combined with atmospheric instability best explain lightning-fire occurrence.