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The preparation of the documents for microfilming required placing either black or white masking around the edges of smaller leaves , to prevent other pages in the volume from showing through . A " moderate " risk in a TC would probably be relatively short-fuse - - in the day-1 period - - and would discuss an exceptional combination of observed or developing intense vertical shear parameters ( such as described by McCaul 1991 ) , with strong forecaster confidence for numerous tornadoes . Prerequisite : STAT 218 or equivalent , and senior or graduate standing . Prerequisite : ME 341 , BMED 410 or consent of instructor . Prerequisite : Senior or graduate standing in engineering or consent of instructor . As applied solely for tornadoes , such as in a TC , it would mean an enhanced probability of tornadoes in series or clusters , and / or " significant " tornadoes ( Hales 1988 and Grazulis 1993 ) producing F2 or greater damage .