Residents of Moore, Okla., had just a 16-minute warning before the devastating tornado first hit ground, just south of town, on May 20. That sobering fact underscores how quickly a twister can strike.

A "tornado warning" means a twister is developing or is actually on the ground. It’s more severe than a "tornado watch," which means conditions are favorable for the development of severe thunderstorms that might spawn tornadoes.

Here’s some advice, culled from AAA and State Farm, on what safety measures your drivers can take if a tornado approaches while they’re on the road. You may want to pass this advice along to them as a reminder.

• Tornadoes can toss cars and large trucks around like toys. Never try to outrun a tornado.

• If you see a funnel cloud or hear a tornado warning issued on the radio or by siren, get out of your vehicle and seek a safe structure.

• Seeking shelter indoors is best, if possible. A basement is safest. Closets or small interior rooms are preferable. Get under a sturdy piece of furniture or mattress and stay away from south and west walls and all windows.

• Do not seek shelter in a mobile home. These structures, even if tied down, offer little protection from tornadoes and should be abandoned.

• If you are caught in the open, with no indoor buildings available to you, find a ditch, ravine or low-lying area and lie flat. Stay away from roadway overpasses. Cover the back of your head and neck with your hands; keep alert for flash floods.

• In general, whenever you're driving during a storm, remember that wet roads mean poor traction. Conditions are most dangerous during the first 10 minutes of a heavy downpour as oil and debris wash away. Driving on wet roads in the rain is just like driving on ice. Take it easy and allow extra time.