Since Grazulis lists only events of F2 intensity or greater, any event not found in his listing has been given a rating of either F0 or F1. Events listed as F2 in the SPC database, but not appearing in Grazulis 1990, are listed here as F1. Notes are included in the narrative of an event if differences were found in the F-scale ratings among the available sources. Nearly two thirds of all tornadoes in OKC have struck during those three months. Strong and violent tornadoes tend to occur slightly earlier, with April the peak month.
Frequencies level off during the summer and autumn before dwindling during the winter.
The time distribution in Fig. Since such events constitute only a small fraction of the total, the difference is not considered to be significant. The frequency of weak events almost certainly has been more constant than the data indicate, but most of the weak events before 1950 probably were not documented. Figure 5 shows the approximate locations and tracks of the tornadoes listed. Exact tracks are difficult to plot in many cases, especially the early ones, since the available data do not provide enough detail.