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<br />Figure 1.1 Colorado's Historical Dry and Wet Periods <br /> <br />DATE DRY WET DURATION (Years) <br />1893-1905 X 12 <br />1905-1931 X 26 <br />1931-1941 X 10 <br />1941-1951 X 10 <br />1951-1957 X 6 <br />1957 -1959 X 2 <br />1963-1965 X 2 <br />1965-1975 X 10 <br />1975-1978 X 3 <br />1979-1996 X 17 <br /> <br />Source: McKee, Doesken and Kleist, 1999 <br /> <br />The 1979-1996 wet period continued through 1999. Since then, Colorado entered another period <br />of significant drought. As of June 2003, Colorado is still being impacted by drought - and even <br />though the 2003 spring has been wetter-than-normal, the drought will continue for at least <br />another year without continued above normal precipitation. (Colorado Climate Center, CSU). <br /> <br />Based on the information above, Colorado has experienced 6 significant droughts in the past 110 <br />years. This equates to a recurrence interval of experiencing a drought every 18.3 years, which <br />lasts, on average, for 6.3 years. <br /> <br />Tornadoes <br />Tornadoes are rotating columns of air marked by a funnel-shaped downward extension of a <br />cumulonimbus cloud whirling at destructive speeds of up to 300 mph, usually accompanying a <br />thunderstorm (Hazards in Colorado). <br /> <br />Tornadoes are ranked according to the Fujita scale, listed below: <br /> <br />Fuiita Tornado Scale <br />FO: 40-72 mph (35-62 kt) <br />Fl: 73-112 mph (63-97 kt) <br />F2: 113-157 mph (98-136 kt) <br />F3: 158-206 mph (137-179 kt) <br />F4: 207-260 mph (180-226 kt) <br />F5: 261-318 mph (227-276 kt) <br /> <br />16 <br />