Tornadoes and Severe Storms

Severe thunderstorms are defined as thunderstorms that produce 1-inch hail or larger and/or strong wind gusts of 58mph or greater. There are about 100,000 thunderstorms each year in the U.S. alone. About 10% of these reach severe levels.

The National Weather Service has a scale for ranking severe storms:

The severe thunderstorm risk categories as defined by the National Weather Service.

Every thunderstorm produces lightning, and can occur without rainfall. Most lighting deaths and injuries occur outside during the summer months.

Tornadoes are violently rotating columns of air that can destroy buildings, flip cars, and create deadly flying debris. March to May is peak tornado season in Middle Tennessee. Although tornados can appear at any time, Tennessee is especially vulnerable and leads the country in nocturnal tornadoes.

The severity of tornadoes are measured using the Enhanced Fujita Scale for tornadoes (see chart below). Based on historical events, in a worst-case scenario it is possible for the extent of a tornado to exceed an EF4 ranking. 

The Fujita tornado scale for ranking tornado severity.


There are several things you can do to prepare in advance for tornados and severe weather:

  1. Sign up for weather alerts through multiple sources. Know the difference between a watch and a warning. Learn about your local tornado warning system.
  2. During storms, look for the following signs:
    1. Dark, greenish sky
    2. Approaching cloud of debris. Loud roar, similar to a freight train
    3. Rotating, funnel-shaped cloud
  3. Designate a tornado “safe room” in your home, and stock it with an emergency tornado kit. Your safe room should be the most protected room in your home, preferably in a basement or interior room on the lowest floor level, with no windows. If you have Storm Shelter installed, add your shelter to the county’s storm shelter registry.
  4. Have tornado plans in place for not only your home but for other locations such as your place of work. Talk about tornadoes with your family so that everyone knows where to go if a tornado warning is issued. Discussing ahead of time helps reduce fear, especially for younger children. Check at your workplace and your children's schools and day care centers to learn about their tornado emergency plans.
  5. If you know severe weather is coming in, prepare your home. Store any yard items that could potentially blow away or cause damage during a severe storm. Make trees more wind resistant by removing diseased or damaged limbs, then strategically remove branches so that wind can blow through.

Stay Alert

It’s important to know the difference between a thunderstorm and tornado watches and warnings:

Severe Thunderstorm Watch

Be Prepared! Severe thunderstorms are possible in and near the watch area.

Severe Thunderstorm Warning

Take Action! Severe weather has been reported by spotters or indicated by radar. Warnings indicate imminent danger to life and property. Take shelter.

Tornado Watch

Be Prepared! Tornadoes are possible in and near the watch area.

Tornado Warning

Take Action!  A tornado has been sighted or indicated by weather radar. There is imminent danger to life and property. Find safe shelter right a


  • Outdoor warning sirens are only meant to be heard outdoors. Don’t rely on sirens as your warning system for while you are at home or inside buildings.
  • Tornadoes can occur even if a watch or warning has not been issued.
  • All tornados have a starting point. If one forms close enough to you, there will be no warning.

The definitions for severe thunderstorm and tornado watches and warnings.

During a Tornado


  1. Stay Weather-Ready: Continue to listen to local news or a NOAA Weather Radio to stay updated about tornado watches and warnings.
  2. Go to a safe room, basement, or storm cellar, away from windows, doors, or exterior walls. This space should be in the lowest level of the building. Put as many walls between you and the outside as possible. Sheds and storage facilities are not safe. Neither is a mobile home or tent.
  3. Use your arms to protect your head and neck.
  4. If you are in a vehicle, the best course of action is to drive to the closest shelter. Remember to buckle your seat belt. If you are unable to make it to a safe shelter, either get down in your car and cover your head, or abandon your car and seek shelter in a low lying area such as a ditch or ravine.
  5. Never try to outrun a tornado in an urban or crowded area in a car or truck. Get out of your vehicle and find sturdy shelter instead.
  6. If you are outside and can safely get to a sturdy building, then do so immediately. If you cannot find shelter during a tornado, find a low, flat location (a ditch or depression) and cover your head with your hands. Beware of the potential for flooding. Do not get under an overpass or bridge.
  7. Watch out for flying debris. Flying debris is the cause of most injuries and fatalities during tornados.
  8. Use your family emergency plan so that you and your family know what you will do, where you will go, and what you will need to take with you to safely weather a tornado. If you are at work or school, follow your tornado drill and proceed to your tornado shelter location quickly and calmly. 

During a Severe Storm

  1. Follow the 30/30 lightening rule. If you can’t you see lightening and can’t count to 30 before hearing thunder, stay indoors for 30 minutes after last hearing thunder.
  2. During severe thunderstorms, unplug appliances and computers to protect them from power surges. Also, losing power can make it difficult to see, and cause tripping hazards.
  3. Avoid taking showers or baths during severe storms. Plumbing can conduct electricity. 
  4. If lightening in nearby and you are driving, stay inside your vehicle. Rubber shoes and tires do not provide protection from lightening, but steel frames of hard-topped cars do as long as you are not touching metal. 
  5. If you are in a forest or open area, seek shelter in a low area under small trees. Be aware of flash floods. Avoid naturally isolated trees, tall trees, hilltops, isolated structures in open areas, or anything metal. If you are on open water, get to land and find shelter immediately.
  6. If you feel your hair stand on end, it means lightning is about to strike. Squat low to the ground on the balls of your feet, hands over ears, and head between knees. Minimize yourself as a target, and minimize contact with the ground. Do not lie flat on the ground.

Immediately After a Tornado

  1. Check for injuries. Call 9-1-1 for medical help, if needed. Victims of lightning strikes carry no electrical charge, and should be attended to immediately. If you’re trapped, use a cloth or mask to protect your mouth, nose, and eyes from dust. You can try to make noise to get the attention of first responders. 
  2. Check power lines. Stay away from fallen power lines or broken utility lines, and report downed or broken lines to your providers. If you haven’t lost power but smell something burning, see frayed or sparking wires, or suspect a gas leak, turn off the main circuit breaker and any natural gas or propane tanks.
  3. Be aware of debris. Don’t enter damaged buildings until you are told they are safe by local authorities. Be aware of hazards from broken glass, nails, and other sharp objects.
  4. Inspect your home. Check for any signs of structure issues, starting with the outside first. Take pictures of all of your home’s damage, inside and out. Collect as much documentation as possible, and save all recovery-related receipts. Fill out our damage survey.

Alert Systems

Using alert systems is crucial to being informed before and during tornado events, just as with any other disaster. Our alert systems page has resources for a number of alert options.

The Red Cross also has a Tornado app that includes tornado alerts and information for your area.

Local Severe Storm and Tornado Risks

History of tornadoes and severe storms in Williamson County

On average, a typical county in Tennessee has about 10 severe storm watches per year. Based on historical records, Williamson County is at risk of tornado events several months each year.

The EF4 tornado that impacted the Rebel Meadows area of Franklin to the Brenthaven area of Brentwood on December 24, 1988 is the largest tornado event ever recorded in Williamson County. The tornado traveled 6 miles with a path width of 150 yards. The destruction left $50 million in damages and led to 1 death caused by a roof collapse.

On January 30, 2015, Middle Tennessee experienced the largest outbreak of tornadic activity in its history. In Williamson County during this outbreak, an EF0 tornado touched down near the intersection of Pinewood Road and Walker Hill Road in southwestern Williamson County where approximately 30 trees were snapped or uprooted and one outbuilding lost part of its roof. The path continued across Highway into an inaccessible portion of Williamson County north of Highway 46. The tornado was reported to be 2.3 miles long and 75 yards wide.

On March 3, 2020, tornadoes cut through downtown Nashville and killed two people in East Nashville. Nashville Severe Weather has a detailed record of the weather progress throughout the day, and provides the example of how sometimes forecasts with a low chance of tornadic activity can change quickly and suddenly with devastating effects.

The following map shows the number of tornadoes by county from 1950-2021.

Number of tornadoes per Tennessee County 1950-2021.

Ranking Local Vulnerability

Williamson County uses simple system called a vulnerability calculator to determine each jurisdiction’s vulnerability to hazardous events, as shown in the charts below.


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