Severe Weather Awareness - Tornado Classification and Safety

 Wisconsin Tornado and Severe Weather Awareness

Part 3 - Tornado Classification and Safety

Tornadoes can occur in many different shapes and sizes ranging from a few yards to over one mile in width.  They can move slowly, appearing nearly stationary, to as fast as 60 mph. The size and shape of a tornado does not necessarily say anything about the tornado's strength or it's capability to inflict damage.  Since tornadoes can change intensity quickly, they should all be considered dangerous.

The vertical winds in tornadoes are capable of temporarily lifting heavy objects such as automobiles or even people hundreds of feet off the ground.  They are also strong enough to carry lightweight objects miles away from their original location.

Tornado Classification

Tornadoes are classified into three broad groups based on their estimated wind speeds and resultant damage:

For over three decades prior to 2007, the most widely used method worldwide for estimating tornado strength and wind speed was the 
F-scale developed by Dr. Theodore (Ted) Fujita. Since 2007 in the U.S., the new Enhanced F-scale has become the standard for 
assessing tornado strength and resultant damage. In the original F-scale, wind speeds were based on calculations of the 
Beaufort wind scale and had never been scientifically verified in real tornadoes.
 

Enhanced F-scale winds are derived from engineering guidelines but still are only judgmental estimates. Because: 

• Nobody knows the "true" wind speeds at ground level in most tornadoes, and
• The amount of wind needed to do similar-looking damage can vary greatly, even from block to block or building to building.

Damage rating is (at best) an exercise in educated guessing. Even experienced damage-survey meteorologists and wind engineers
can and often do disagree among themselves on a tornado's strength.

More information on the Fujita and Enhanced Fujita Tornado Rating System.

Recent Violent Wisconsin Tornadoes 

Even though 80% of Wisconsin's tornadoes have been rated weak in intensity, Wisconsin has experienced 3 tornadoes with winds 
speeds in excess of 260  mph since 1950. One of these violent tornadoes occurred as recently as 1996, peaking in strength east 
of the village of Oakfield in Fond du Lac county. Violent tornadoes account for 70% of all tornado deaths in the U.S.

Tornado Safety

• Preparation
  • Know the county you live in. The NWS issues Tornado Warnings that are polygon-based, and may include an entire county, or more likely portions of neighboring counties.
  • Stay abreast of the latest forecast via NOAA Weather Radio, commercial radio or TV.  Keep a watchful eye on the sky, and consider postponing outdoor activities.
  • Know your communities warning system.  Communities have different ways of warning residents about tornadoes, with many having sirens intended for only outdoor warning purposes.
  • Pick a safe room in your home where household members and pets may gather during a tornado.  This should be a basement, storm cellar, or an interior room on the lowest floor with no windows.
  • Practice periodic tornado drills so that everyone knows what to do if a tornado is approaching.
  • Prepare for high winds by removing diseased and damaged limbs from trees.
  • Move or secure lawn furniture, trash cans, hanging plants or anything else that can be picked up by the wind and become a projectile. 
  • Watch for tornado danger signs:
    • Dark, often greenish clouds/sky
    • Wall Cloud - an isolated lowering of the base of the thunderstorm
    • Debris cloud
    • Large hail
    • Funnel Cloud
    • Roaring Noise
• During a Tornado
  • Safest place to be is an underground shelter, basement or safe room. Cover your head with your arms, a mattress, or heavy blanket.
  • If no underground shelter is available, a small, windowless interior room or hallway on the lowest level of a sturdy building is the safest alternative.
  • Stay away from windows!
  • Get out of large auditoriums or large warehouses.
  • Mobile homes are not safe during tornadoes or severe winds (nearly 40 percent of all tornado-related deaths come from residents of mobile homes).  Do not seek shelter in a hallway or bathroom of a mobile home. If you have access to a sturdy shelter or a vehicle, abandon your mobile home immediately.  
  • If you are caught outdoors, seek shelter in a basement, shelter, or sturdy building.  If you cannot quickly walk to a shelter:
    • Immediately get into a vehicle, buckle your seat belt and try to drive to the closest sturdy shelter.
    • If flying debris occurs while your are driving, pull over and park.  Now you have the following options as a last resort:
      • Stay in the car with the seat belt on.  Put your head down below the windows, covering with your hands or a blanket if possible.
      • If you can safely get noticeably lower than the level of the roadway, exit your car and lie in that area, covering your head with your hands. 
  • Never drive directly toward a tornado or in the vicinity of a tornado.  Any tornado can change direction or speed quickly and put you at risk.  Drive at right angles away from the tornado or get out of your vehicle and seek shelter immediately.
  • Highway over-passes are not necessarily the safest outdoor place to be.  People have been killed while hiding underneath an over-pass as a tornado moved overhead.  Instead, seek a sturdy shelter or lie flat on the ground and cover your head with your arms. 
•  After a Tornado
  • Continue listening to local news or a NOAA Weather Radio for updated information.
  • Stay out of damaged buildings.
  • Watch out for fallen power lines or broken gas lines and report them to the utility company immediately.
  • Take pictures of damage, both of the building and its contents for insurance claims.
  • Clean up spilled medications, bleaches, gasoline and other flammable liquids that could become a fire hazard. 

More Safety rules from Ready.gov/tornadoes.