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6 <br /> TORNADO INTENSITY SCALE <br /> Category Definition - Effects <br /> FO Gale Tornado - 40-72 MPH. Some damage to chimneys; <br /> broken branches and tree limbs; some shallow rooted or <br /> weak trees blown over; signs and billboards damaged. <br /> F1 Moderate Tornado - 73-112 MPH. This is also the lower <br /> limit- of hurricane force winds; shingles or tin peeled <br /> off roofs; ' mobile homes pushed off foundations or <br /> overturned; moving vehicles blown off the road. <br /> F2 Strong Tornado - 113-157 MPH. Roofs torn off frame <br /> houses; mobile homes demolished; large trees snapped or <br /> uprooted; railroad boxcars pushed over; light-object <br /> missiles generated. <br /> F3 Severe Tornado - 158-206 MPH. Roofs and some walls torn <br /> off well-constructed houses; train cars overturned; heavy <br /> vehicles lifted off the ground and thrown; most trees in <br /> forest blown down. <br /> F4 Devastating Tornado - 207-260 MPH. Well-constructed <br /> houses leveled; structures with weaker foundations blown <br /> some distance away; heavy vehicles thrown and large <br /> missiles generated. <br /> F5 Incredible Tornado - 261-318 MPH. Strong frame houses <br /> lifted off foundations and carried considerable distance <br /> to disintegrate; automobile sized missiles fly through <br /> the air in excess of 100 yards; trees debarked; <br /> incredible damage phenomena will occur. <br />