Understanding the difference between a tornado watch and a tornado warning is crucial for ensuring your safety in a severe storm. Think of a tornado watch as a yellow traffic light that raises your awareness, while a warning is a red light that requires immediate action.
- A tornado watch means weather conditions are favorable for tornado formation. But, there is no tornado present.
- A tornado warning means there either is a tornado or else one is imminent.
Tornado Watch vs Warning: Which Is More Dangerous?
A tornado warning is more dangerous than a tornado watch, as it indicates that a tornado is imminent or already occurring. If a tornado warning is issued for your area, take immediate action to protect yourself and your family.
The National Weather Service (NWS) issues a tornado watch when conditions are favorable for the formation of tornadoes in a particular area. A tornado watch typically lasts for several hours and covers a large geographical area. It does not mean that a tornado has been spotted. A tornado watch does not always lead to a tornado warning.
What to Do During a Tornado Watch
- Stay informed: Keep an eye on your local news channels or NOAA Weather Radio for updates on weather conditions, and be prepared to act if a tornado warning is issued.
- Locate or prepare your emergency kit: Make sure you have an emergency kit with essential supplies like food, water, medications, and a flashlight with extra batteries. If you have pets, have a plan for transporting and caring for them, too.
- Be ready to seek shelter: Identify the safest location in your home, such as a basement, interior room, or a small, windowless space on the lowest level of your building. If you are outdoors and can’t get inside, identify a low-lying, protected area.
- Communicate with your family: Make sure everyone in your household knows the tornado safety plan and where to go in case of a tornado warning. Check in with friends or relatives who may need assistance.
A tornado warning is an urgent alert issued by the National Weather Service when a tornado has been sighted or indicated by radar. This means that there is an immediate threat of a tornado in the warned area, and you should take action to protect yourself and your family. While a tornado watch covers a large area, a warning is localized. Usually, a watch precedes a warning. But, sometimes a tornado warning occurs without a watch being in effect.
What to Do During a Tornado Warning
- Seek shelter immediately: Go to your pre-identified safe location or the lowest level of your building, away from windows, doors, and outside walls. Cover yourself with a mattress, heavy blankets, or cushions to protect yourself from flying debris.
- Do not try to outrun a tornado in a vehicle: If you are in a car, pull over, and find the nearest sturdy building or shelter. If no shelter is available, park you car and find a low-lying area such as a ditch or ravine, lie flat, and cover your head. Do not seek shelter under an overpass because the constricted space funnels wind and debris.
- Stay informed: Continue monitoring your local news or NOAA Weather Radio for updates on the tornado’s path and when it is safe to leave your shelter.
How to Recognize Tornado Conditions
Tornadoes often accompany severe thunderstorms and can form rapidly. Conditions that may indicate a tornado include:
- A dark, greenish sky
- Large, low-lying clouds, particularly if they are rotating or dip down into a pointed shape
- A loud roar, similar to the sound of a freight train
- Hail or heavy rain followed by a sudden calm or a rapid shift in wind direction
The Green Sky Phenomenon
The green sky phenomenon associated with tornadoes is not entirely understood, but there are a few theories. One explanation is that the greenish hue results from the scattering of sunlight by the storm’s heavy precipitation, such as rain and hail. The sunlight interacts with the water droplets and ice crystals, scattering the shorter wavelengths of light (blue) and leaving the longer wavelengths (green and red) to be seen. When clouds are dense, more light filtering occurs and the green color is more noticeable. At sunrise or sunset, tornadoes produce green skies when the gold or red light interacts with the dark blue clouds, leaving green.
Sudden Calm Before a Tornado
A sudden calm before a tornado comes from the behavior of the storm system. Tornadoes often form at the edge of a severe thunderstorm, where there is a sharp contrast between the warm, moist air feeding the storm and the cooler, drier air behind it. As the warm air rises and the cold air sinks, a circulation can develop, leading to the formation of a tornado. When this circulation reaches the ground, it often causes a temporary drop in wind speed at the surface, creating a brief period of calm before the tornado arrives. But, some tornadoes occur during intense thunderstorms, without any preceding calm air.
Safe Shelter During a Tornado or Severe Thunderstorm
The safest place to seek shelter during a tornado or severe thunderstorm is a sturdy building with a well-constructed basement. Otherwise, seek an interior room on the lowest level, away from windows and outside walls. In public buildings, like schools or shopping centers, avoid large open areas like gymnasiums or atriums. Instead, opt for small, enclosed rooms or interior hallways. If you are in a mobile home, evacuate and seek shelter in a nearby sturdy building or designated storm shelter.
National Weather Service Alert Methods
The National Weather Service uses a combination of methods to alert the public about tornadoes:
- Weather Radio: The NWS operates a network of NOAA Weather Radio stations that broadcast continuous weather information, including tornado watches and warnings. Local radio stations also broadcast warnings.
- Wireless Emergency Alerts (WEA): The WEA system sends tornado warnings and other critical alerts directly to compatible cell phones within the affected area, even if the user is not subscribed to the service.
- Television: Local television stations relay tornado watches and warnings issued by the NWS, often accompanied by on-screen maps and real-time updates.
- Social media and online resources: The NWS and other weather agencies maintain active social media accounts, providing real-time updates on severe weather events. Many also offer email or text message alert subscriptions for localized warnings.
- Outdoor warning sirens: In some communities, outdoor warning sirens alert residents. These sirens typically activate when a tornado warning is issued or when trained spotters confirm a tornado.
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- “Criteria for public weather alerts“. Environment and Climate Change Canada.
- “Highway Overpasses as Tornado Shelters“. National Weather Service. National Oceanic and Atmospheric Administration.
- Mathis, Nancy (2007). Storm Warning: The Story of a Killer Tornado. Touchstone. pp. 41–43. ISBN 978-0-7432-8053-2.