Tornadoes

Stoughton Wisconsin Tornado of August 18. 2005

Stoughton Wisconsin Tornado of August 18. 2005

An average of 21 tornadoes occur each year in Wisconsin… but some counties can have many tornado-free years in a row. On average, 1 person dies each year from tornado-related injuries. Tornadoes are a violently rotating column of air (circulation) extending from the cloud base to the ground. However, funnel clouds are defined as not touching the ground.

Peak tornado season is May through August, but tornadoes have occurred in every month but February. Most tornadoes occur between noon and 9 PM.. with 5 PM a favored time. Most Wisconsin tornadoes travel southwest to northeast or west to east, travel at speeds of 20 to 40 mph, and persist for less than 10 minutes with a path length of less 5 miles.

Roughly 80% of Wisconsin’s tornadoes are weak with wind speeds of 65 mph. About 19% are rated as strong with wind speeds of 111 to 165 mph. Luckily, only 1% are violent with wind speeds 166 mph or higher.

Tornado Basics

Tornadoes are one of the most powerful and violent storms that nature can produce.  They come in all shapes and sizes and can occur in every state, on any day and at any hour.  All tornadoes can be a direct threat to your safety.  Each year they constitute a major hazard across the U.S.

A tornado is a violently rotating column of air (wind) that extends from the base of a cumulonimbus cloud down to the ground.  One cannot see a column of air and wind that is rotating on a vertical axis between the cloud base and the ground unless there is a visible condensation funnel inside the invisible tornado, or one sees rotating dirt/debris at the ground level.

There have been many documented cases in which a tornado was damaging structures and vegetation but there was very little or no visible condensation funnel.  Most people refer to the condensation funnel as a funnel cloud.  Since you can have a tornado with little or no visible condensation funnel, the condensation funnel is not the tornado.

For many years it was assumed that tornadoes grew downwards from the base of a cumulonimbus cloud to the ground because the condensation funnel visibly grew downwards.  Consequently, this gave people the false perception that tornadoes touched down.  It is true that the condensation funnel does grow downwards, but a nearly invisible tornado can develop between the cloud base and ground prior to the development of a condensation funnel.  In most cases, eventually a condensation funnel does develop from the cloud base down to the ground, but this may happen after a tornado has already caused damage.

Wisconsin Tornado Statistics

  • Peak tornado season is May through July.
  • Peak hours are between 3 pm and 9 pm but can occur at any time.
  • Peak hour is between 6 pm and 7 pm.
  • Average of 23 tornadoes annually.
  • Average of 1 fatality each year due to tornado-related injuries.
  • Average tornado lasts about 7.1 minutes and has a path length of about 3.7 miles and path width of about 118 yards.
Tornado Events, Deaths, and Injuries in Wisconsin 1982-2012

Tornado Events, Deaths, and Injuries in Wisconsin 1982-2012

Tornado Watch vs. Tornado Warning

Be sure you understand the difference!  Many people confuse watches and warnings.

  • A tornado watch is issued to give you advance notice that the development of tornadoes is possible in your area.  This gives you the time to make plans for moving to a safe shelter quickly if a tornado is sighted.
  • A tornado warning is an urgent announcement that a tornado has been reported by a person or is imminent due to Doppler Radar information.  Take immediate action.  Move quickly if you are in the tornadoes path.  Seconds can save your life.

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

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. T. Theodore 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 Fujita Scale Ratings

Enhanced Fujita Scale Ratings

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. 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.
Extensive tornado damage was found across many areas of the Midwest and Gulf States, including in Kenosha County during a major January tornado outbreak.

Extensive tornado damage was found across many areas of the Midwest and Gulf States, including in Kenosha County during a major January 2008 tornado outbreak.

Tornado Myths

Many myths exist about tornadoes. If followed, these myths could be life-threatening. Several of these myths are listed below.

  1. Seek Shelter under an Over-Pass
    • Stopping under a bridge to take shelter from a tornado is a very dangerous idea, for several reasons:
    • Deadly flying debris can still be blasted into the spaces between bridge and grade, and impaled in any people hiding there.
    • Even when strongly gripping the girders (if they exist), people may be blown loose, out from under the bridge and into the open, possibly into the tornado itself. Chances for survival are not good if that happens.
    • The bridge itself may fail, peeling apart and creating large flying objects, or even collapsing down onto people underneath. The structural integrity of many bridges in tornado winds is unknown–even for those which may look sturdy.
    • Whether or not the tornado hits, parking on traffic lanes is illegal and dangerous to yourself and others. It creates a potentially deadly hazard for others, who may plow into your vehicle at full highway speeds in the rain, hail, and/or dust. Also, it can trap people in the storm’s path against their will, or block emergency vehicles from saving lives.
  2. Tornadoes Never Strike Twice
    • Cordell Kansas was struck by a tornado on May 20th, three years in a row (1916, 1917, 1918). In Guy Arkansas, three tornadoes hit the same church on the same day.
  3. Big Cities and their Tall Buildings are Protected from Tornadoes
    • Many cities in the U.S. have been directly hit by tornadoes in recent years including Miami, Salt Lake City, Birmingham, Oklahoma City, Houston, Fort Worth, Nashville and Joplin MO.
    • Tornadoes are typically 5 to 10 miles tall. A tall building with a height of 500 to 1000 feet can not deflect or destroy a tornado.
  4. Large Lakes Protect Nearby Areas from Tornadoes
    • While cold water and the cool air on top of the lake can provide a locally stable environment, chances are a thunderstorm producing a tornado moving toward a cold lake has something much larger driving it than the cold water can inhibit.
    • Typical lake breezes found along the Lake Michigan shore are often shallow and only affect a small portion of the lower atmosphere. Warm and unstable air above this marine layer/lake breeze could very well sustain a thunderstorm’s strength. For example on March 8, 2000 Milwaukee County experienced its earliest tornado on record at a time when Lake Michigan is climatologically coldest. On August 8, 2011, a weak tornado developed on Lake Monona in the city of Madison. It stayed over the lake as a waterspout and did not cause damage. This weak waterspout was associated with a rain-shower. There were no thunderstorms in the area.
  5. Mountains, River Valleys and Large Lakes Inhibit Tornados and/or cause Splitting Storms
    • While conditions would not be optimal for tornado development on top of mountains or over Lake Michigan, tornadoes have been documented to cross the Appalachian Mountains and cross a 10 thousand foot tall mountain in Yellowstone National Park. Strong tornadoes have also crossed the Mississippi River and other large rivers and lakes.
  6. Seeking Shelter in the Southwest Corner of your Home will Protect you from Flying Debris
    • This myth was devised slowly by the misconception that all tornadoes move to the northeast. Therefore as the tornado hits your home, all the debris would be directed to the northeast, away from you. Since tornadoes can move in any direction, this myth is false.
    • The SW corner is no safer than any other part of the basement, because walls, floors and furniture can collapse (or be blown) into any corner.
    • Debris such as motor vehicles can also be pushed into the basement by a tornado. You should position yourself under the I-Beam or a heavy work bench in your lowest level to increase your chances for survival.
    • During a tornado warning, seek shelter in an interior room on the lowest level of the building, away from windows, and if possible, under a sturdy piece of furniture or staircase.
  7. Open Windows Prior to Tornado Strike to Equalize Pressure Inside the House to Prevent it from Exploding
    • Opening the windows is absolutely useless, a waste of precious time, and can be very dangerous. Don’t do it. You may be injured by flying glass trying to do it. And if the tornado hits your home, it will blast the windows open anyway.
  8. Tornadoes Only Occur in the Late Spring and Summer in Wisconsin
    • While the optimal time for tornadoes in Wisconsin is May through July, tornadoes can develop at any time of day and at any time of year. Since 1950, tornadoes have occurred in Wisconsin during every month but February, however it’s only a matter of time.
  9. The Shape and Size of the Tornado Determines it’s Strength
    • Tornadoes come in all shapes and sizes and you should not correlate the size of the tornado with its strength. The only way to determine the strength of the tornado is through damage assessments, or by taking a direct measurement of the wind. During damage assessments, National Weather Service personnel look for clues that will tell them how strong the winds were. The wind estimate (or measurement) is then related to the Enhanced Fujita (EF) Tornado Scale, and a tornado intensity level will be assigned to the tornado. Tornadoes are rated on a scale from EF0 to EF5.
    • Merely by looking at the tornado’s shape does not reveal it’s strength. The visible funnel of the tornado is created by condensation or dirt and debris. Conditions that create the visible funnel will change each time a tornado develops, and therefore the funnel appearance can not be reliably used as a strength indicator.
  10. Significant Property or Crop Damage is Always a Result of a Tornado
    • Tornadoes can produce significant damage, however straight-line winds can be just as destructive. Down-burst winds associated with severe thunderstorms are capable of reaching wind speeds of 100 to 150 mph, or the equivalent of an EF1, EF2, or EF3 tornado. Significant damage does not always imply a tornado.
  11. Mobile Homes attract Tornadoes
    • Of course not. It may seem that way, considering most tornado deaths occur in mobile homes, and that some of the most graphic reports of tornado damage come from mobile home communities. The reason for this is that mobile homes are, in general, much easier for a tornado to damage and destroy than well-built houses and office buildings. A brief, relatively weak tornado which may have gone undetected in the wilderness, or misclassified as severe straight-line thunderstorm winds while doing minor damage to sturdy houses, can blow a mobile home apart. Historically, mobile home parks have been reliable indicators, not attractors, of tornadoes.
  12. The Number of Tornadoes have been Increasing due to more Favorable Weather
    • The number of tornadoes in the U.S. has increased since the pre-1950 years. However this increase is most likely due to the general increase in the population, more trained storm spotters, better radar detection, more cameras, and better follow-up damage surveys.

More Information

More Information about tornadoes and other weather events is available from the National Weather Service.

Click on the image above for an informative brochure aboutThunderstorm, Tornado, and Lightning Preparedness.

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