Before I proceed to cover the subject of tornado safety in the home in detail, I need to cover the types of severe weather statements issued by the National Weather issues and the reasons behind them. Even today, many people tend to become confused by these statements, a fact which sometimes leads them to disregard these statements altogether. As a result, it is little wonder that, especially in recent years, the National Weather Service has taken a close look at the wording of their severe weather statements, and is working hard to both clarify them and to better convey how the public should respond to each of them when severe weather does strike. Since tornadoes are my primary focus at this point in this blog, I will concentrate on tornado-related statements this time around, with links to other sources of information on related topics.
Whenever it is determined that severe weather is in the making, the National Weather Service will issue one of several different types as conditions warrant: WATCHES (to give you time to prepare), WARNINGS (to tell you it is time to act), PDS, or "Particularly Dangerous Situations," (when the potential for severe weather is unusually high, or when an outbreak is expected to be unusually intense), and, finally, "Emergency" (meaning an extreme, life-threatening situation that requires IMMEDIATE action or response).
The first of these is the Severe Weather WATCH. This type of severe weather statement is usually the first such statement, in sequence, to be issued. It indicates that conditions either already are, or are expected to become, favorable for the development of severe weather. All Severe Weather Watches are issued by the Storm Prediction Center in Norman, Oklahoma, usually several hours or even as much as a day or more in advance. Because of the scale of the weather systems involved, a Severe Weather Watch will usually cover thousands of square miles, and generally will cover a time span of from five to eight hours.
If a severe weather event is expected to be unusually strong or dangerous, the notation, "Particularly Dangerous Situation" will be added to the original message text. This also means that a larger amount of territory will be included than a "regular" Severe Weather Watch, and will run for a longer period of time as well.
When a severe weather event is determined to either be imminent or has actually been detected, a Severe Weather WARNING will be issued. Because such events are almost always local in nature, a Severe Weather Warning is almost always issued by a local office of the National Weather Service, and will cover a much smaller area than a Severe Weather Watch, and will last for a much shorter period of time. Again, the terms "Particularly Dangerous Situation" or "Emergency" (in the case of a tornado) may be added to the original text to indicate greater than normal or even extreme levels of severity or danger. In particular, the term, "Tornado EMERGENCY" means that an extremely dangerous, life-threatening tornado has either been spotted by trained storm spotters, detected on weather radar, or both, and that you should take IMMEDIATE action to protect yourself!
For more information on this subject, I invite the reader to consult Wikipedia, under the term, "Severe Weather Terminology."