A number of studies have been made over the years in an attempt to relate pertinent weather factors (including fuel moisture) to fire occurrence. Generally, regression analyses were used. In such studies, all of the many factors that affect ignition of wildfires are necessarily included. Such studies have been useful, and in fact we will use results from them to devise an index of ignition probability, but the results do not lend themselves to improvement by further research. The only recourse is to redo the studies with different data. The following development is an attempt to dissect ignition probability into its component parts. In this way, the place in the overall scheme of things where studies such as Blackmarr's (1969) fit, can be shown. In this way also, the places where knowledge is lacking and assumptions need to be made, can be pointed out. Hopefully, future research can then tackle specific components and make improvement of our determination of ignition probability possible.