GEO 125

Physical Geography

Tornadoes

General Atmospheric Conditions Associated with Tornadoes

  • Warm air

  • Moist air

  • Rising air

  • Unstable air

  • Vertical air movement

  • Cumulonimbus clouds

Weather Associated with Tornadoes

  • Cold fronts

  • Summertime convectional storms

  • Hurricanes

Temporal Characteristics Associated with Tornadoes

  • Majority of tornadoes occur in the afternoon

  • Majority of tornadoes occur in the spring of the year primarily in April and May in conjunction with the passage of cold fronts

Physiographic Characteristics Associated with Tornadoes

  • Most tornadoes occur over land (a similar type of meteorological event called a water spout can be formed over large water bodies)

  • Most tornadoes occur over flat terrain rather than in mountainous areas

  • Most tornadoes occur over nonforested areas

Geographic Distribution of Tornadoes

  • Ninety percent of all tornadoes (800 to 1200 annually) occur in North America due to the north to south trend in the major mountain chains that allow for the contact of continental polar air and maritime tropical air during the spring of the year

  • The state with the greatest number of tornadoes annually is Oklahoma

General Characteristics Associated with Tornadoes

  • Funnel cloud versus a tornado

  • Atmospheric pressure at least 10% below ambient atmospheric pressure

  • Counter clockwise rotation of the storm

  • Wind speeds up to 300 miles per hour possible but most storms have wind speeds in the vicinity of 100 miles per hour

  • The highest wind velocities normally occur on the eastern side of the storm

  • Most tornadoes are normally less than 1/4 of a mile in diameter, but extremely large storms may be as much as one mile across

  • Most tornadoes are on the ground for about 15 minutes, but some have been reported to be on the ground for over an hour

  • Most tornadoes travel on the ground for only about 15 miles, but some have been reported to have traveled several times that distance

  • Tornadoes normally are associated with a family of storms which often leaves the false impression that one storm has been on the ground for several hours and has traveled several miles

Mitigation Strategies to Reduce the Tornado Hazard

  • Warnings issued by NOAA or local authorities

  • Tornado watches are issued when the conditions are considered to be right for the possible occurrence of a tornado
  • Tornado warnings are issued when a tornado has been sighted
  • Use of doppler radar
  • Use of national lightning detection system
  • Use of tornado shelters
  • Use of warning sirens
  • Individual strategies

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