- Tornado Watch - This indicates that conditions are right for tornadoes, but none has been observed. Monitor conditions and listen for further alerts.
- Tornado Warning - A tornado or funnel cloud (a precursor to a tornado's touching down) has been spotted or is indicated by radar. This is when tornado sirens may begin. Seek shelter immediately. When a powerful tornado is headed for a densely populated area, the NWS issues a Tornado Emergency to stress the severity.
Some local areas have tornado sirens and lights, especially in Tornado Alley and other regions where tornadoes are a seasonal occurrence. If you hear what sounds like an air raid siren, this is probably a tornado siren sounding, and you should seek shelter immediately. Many communities periodically test these systems at a set time, such as at exactly noon on a weekday of the first week of each month, so check the time and the skies (tornadoes do not develop in sunny weather) before panicking. (Most communities will skip these tests if the weather is stormy, to avoid causing undue alarm.)
Heavy rain and hail can hide a tornado from view. This is especially likely in the more humid regions of the southern and eastern US. Tornadoes will also be very difficult to see at nighttime, unless backlit by frequent lightning. The roar of a tornado (similar to a freight train or a jet aircraft taking off) may be the only sign that one is approaching.
There are some specific signs that a tornado is developing or likely:
- Debris - If you see a cloud of debris being swept into the air in the distance, that could mark the position of a tornado even if you don't see the funnel cloud.
- Green Clouds - Green clouds are normally seen when there is a large amount of ice in the clouds. This is an indication of hail and could be a warning that a tornado is likely.
- Hail - Hail will sometimes occur. The larger the hail the more likely that there may be a tornado associated with the storm.
- Rotation - If you see rotation in the clouds (not just a swirl of wind near ground level, which is an entirely different phenomenon), that may indicate the presence of a tornado or the possibility of a tornado developing.
Day or night, A loud continuous roar or rumble which doesn't fade in a few seconds like thunder or a train could indicate a tornado.
Go to the lowest floor or center of the building away from windows and close to an interior wall. Crouch down and cover your head. Do not get in the elevator; you'll be trapped if the electricity goes out, and there's always a chance that the lift mechanism will give out if the roof is damaged. If you're not too high, use internal stairways to reach the ground floor or basement. Stairwells are probably one of the safer places to seek shelter in such circumstances anyway (i.e. no windows, sturdy construction).
The least safe place to be is inside something the tornado can pick up; you're actually better off outside.
If you are in a mobile home and there's a tornado warning, you should seek out the nearest storm shelter or protected building. People morbidly joke that mobile homes and trailers must somehow attract tornadoes because they are so often shown on TV as twister disaster areas; the serious truth is that their vulnerability is why they make for the most sensational news clips. Studies have shown that a mobile home is the worst place you can be during a tornado; the broad sides of the structure are like a sail in the wind, and there's nothing to hold them in place. It may sound counterintuitive, but you should leave the mobile home and get in a ditch, culvert, or drain pipe, low to the ground. If you are staying in a mobile home and trailer park ask management if there is a tornado shelter close by. These may be cellars or sturdy buildings.
If you are in your automobile and you see a tornado coming, don't try to out-run it; tornadoes can easily outrun a car driving into a 100-mph headwind. Your safest option is to leave the car and get in a sturdy building. If that is not available, get out of the car and get in a low area such as a culvert, drain pipe or ditch. If you are staying in your car, attempt to drive at right angles to the tornado to get out of its path. If the tornado does not appear to be moving left or right, chances are it is coming straight for you. A car is probably safer than a mobile home (less wind-catching surface to drag it into the air), but it's still safer to get out and hunker down low. The best option is to find a ditch to lie flat in, and cover up.