Tornadoes form during thunderstorms, when warm and cool air masses collide. This results in strong winds that begin to rotate in a column reaching the ground at speeds anywhere between 100 to 500 miles per hour. Tornado funnels can be spotted when condensation, dust and debris collect in the wind. Sometimes, they can be accompanied by heavy rain or hail. A tornado itself may be a relatively small storm, with the average width being 300 to 500 yards—but they can travel across dozens of miles before wind speeds drop.
Scientists are still studying the physics of how and when tornadoes form: not every thunderstorm that presents the right conditions for a tornado causes one. Meteorologists at the National Weather Service can issue tornado watches several hours ahead of a potential storm. A watch indicates that a tornado might occur near you because of weather conditions. A tornado warning is issued when a tornado has been spotted, either on radar or by storm spotters, and a serious threat is present. You may not have much time to prepare once a warning is issued.
Tornadoes can occur almost anywhere, anytime
In North America tornadoes tend to occur in the southern plains from May to June; early spring along the Gulf Coast; and June and July in the Midwest.
It’s possible for tornadoes to form well outside of a “season.” In December 2021, tornadoes struck parts of Kentucky and Tennessee, causing massive damage and loss of life. It’s a myth that tornadoes don’t strike urban areas: They can touch down anywhere. This year, for example, tornadoes struck Austin and New Orleans in March.
Look out for tornado signs
Tornadoes can occur suddenly, with little warning. Here are some tell-tale signs that you should seek shelter immediately:
- If you see a funnel shaped cloud extending towards the ground in your vicinity
- If you hear winds that sound like a loud roar, similar to a train or high pitched whistles
- If the sky changes colors and appears green or yellow
Measuring tornado strengths and damage
Unlike other storms, like hurricanes and tropical storms, the strength of a tornado is usually determined after it strikes. This is because of the difficulty of measuring wind speeds during the short, unpredictable storms. Instead, meteorologists assess the damage left behind, and estimate wind speeds based on that, using the Fujita Scale.
How to stay informed and prepared
Ahead of a storm, conditions may change rapidly. Tornadoes are also extremely unpredictable. Having the most accurate information could save your life and help you prepare for whatever is on the horizon. Here are some emergency alert services:
- Wireless Emergency Alerts: These emergency alerts will appear as a text notification on your phone, with a unique sound and vibration pattern. The alerts are sent by National Weather Service stations or state and local public safety agencies, based on your location. You do not have to subscribe to these alerts, and almost every cell service provider allows these messages to be sent to your phone for free. (If you are not receiving alerts, you may need to enable them through the settings on your smartphone.) Some older phones can’t receive wireless emergency alerts.
- State, county or city emergency alert services: This service will vary by your location. Some local agencies provide texts or email notifications that you must subscribe to. For example, to sign up for New Orleans’ local emergency alerts, you can text NOLAREADY to 77295 or sign up for the city’s newsletters through a portal. These services are free.
- Social media posts from local agencies are also a trusted source of information. However, depending on your agency’s capacity, they may not be able to provide real time alerts.
- NOAA Weather Radio: If you do not have cell or internet service during a disaster, you may not be able to get other types of emergency alerts on your phone or computer. NOAA Weather Radios can connect to the frequency where the National Oceanic and Atmospheric Administration broadcasts emergency alerts 24/7 over the radio. You will only receive these alerts if your radio is specifically compatible, so be sure to check product reviews before purchasing a radio. (Source: NOAA, Popular Mechanics)
Make a plan ahead of time: Have emergency supplies with you, know where your important documents and items are, and remember to check in on friends and family.
Sheltering in place
You can be seriously injured or die during a tornado if you are hit by debris or get caught in a collapsing structure during the storm. The safest place to go during a storm is a basement. If you do not have a basement— many homes in the South do not—the next safest option is to shelter in place on the lowest floor of your house in an interior room without any windows, like a closet, bathroom or central hallway. If you live in a multi-story apartment building, shelter in a common area or with neighbors on the ground floor. If possible, make a plan with your neighbors or coworkers ahead of time to have a place to meet for shelter.
If you are in a public place, such as a school, mall or gym, follow the same guidelines and any directions from emergency personnel who may be present. If you are on the road, find shelter indoors immediately.
Cover your head and neck from falling debris. In a home, you can use a mattress or take shelter under a sturdy table, bench or other structure.
Evacuating from mobile homes
Typically, evacuations are not recommended during a tornado watch or warning. That’s because the storm’s path is unpredictable, and being caught outside or in a car during the storm could be more dangerous. However, the CDC recommends that if you live in a mobile home, you should find alternative shelter immediately when your area is under a tornado warning. That’s because these structures are the most vulnerable to a tornado’s high winds, even if the home is tied down.
Make a plan ahead of time so that you know where you’ll go if a tornado warning is issued for your area. This could include finding shelter at the nearest safe building, such as a school, place of worship, public library, or at the house of friends or family. Pack an evacuation kit with your essential items and documents, too, in case your house is damaged.