The American Red Cross has several reference guides to help you prepare for many different emergency situations. You should be prepared at home, at work, and at school for everything from a simple power outage to severe weather to the possibility of terrorist action. If you own a business, the Red Cross also has information on how to protect your employees and your business.
The National Weather Service (NWS) has information about severe weather events such as thunderstorms, tornadoes, and flooding, including a good brochure (PDF) that explains how to be ready for these situations.
The NWS operates a network of radio stations that serve the public 24 hours a day, 7 days a week to provide weather information. When you buy a weather radio with an alert capability, the radio can let you know when severe weather is approaching.