from the base of the CB cell. As the funnel develops, itwill gradually assume the more common cone-shapedappearance. When the funnel cloud (fig. 1-16) extendsdownward from the CB base to a point where its circularrotation reaches the ground, it is then called a tornado(fig. 1-17). Funnel clouds and tornados containdestructive, concentrated, cyclonic winds in excess of150 knots. The force of the wind is amplified by therapid change in the direction of the winds as the tornadopasses over an area. Estimates based on damage equatethe force of tornados to straight-line winds of near 500miles per hour. Funnel clouds can be seen due to thevisible moisture from the parent cloud. Under a funnelcloud, the rapidly circulating winds may be invisibleuntil the circulation picks up dust and debris fromearth’s surface.Waterspouts (fig. 1-18) develop over warm oceanor bay waters more frequently than overland. Theyhave been observed from the bases of rapidly buildingtowering cumulus cells, often without any precipitationoccurring. They are generally weaker than tornadoes,but still contain dangerous, destructive winds.Figure 1-17.—Tornado.When conditions are favorable for tornadodevelopment, waterspouts may be assumed to be asstrong as a tornado.But when conditions are NOTfavorable for tornadic development, then anywaterspouts that form are usually less powerful. AGreat Lakes freighter, S.S. Edmond Fitzgerald, was lostFigure 1-16.—Funnel clouds.Figure 1-18.—Waterspout.1-16
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