by an ugly column of dust and debris, sucked up from the ground and thrown outward by the centrifugal force of the whirl. The funnel begins as a vertical column, but the upper portion of the whirl sometimes becomes slanted and detached as the mother cloud moves on. Several funnels may build down from the mother cloud, but all of these may not reach the ground. The diameter of the tornado can vary from a few meters to a few hundred meters, with an average of about 250 meters. The winds outside the funnel cloud are also strong, and the width of the path may be two to four times as wide as the funnel cloud, based on the destructive effects on the ground. The passage of a tornado may be accompanied by a sudden pressure drop. The decrease in pressure from the rim to the center of the tornado causes a tremendous force that few buildings can withstand. The outside pressure of the building drops as the tornado passes over. This drop is so sudden
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