- A branch of the National Centers for Environmental Prediction, the Storm Prediction Center (SPC) issues tornado watches for the continental United States. The SPC is located in Norman, Oklahoma. Local branches of the National Weather Service (NWS) issue tornado warnings. Because NWS offices are regional, they are able to provide more accurate reports on local weather as it occurs. There are over 100 NWS offices serving the United States. These local NWS offices are responsible for cancelling all tornado watches and warnings.
- A tornado watch applies to approximately 25,000 square miles and covers a relatively long span of time. For example, on May 3, 1999 the SPC issued a tornado watch for western and central Oklahoma. This watch was in effect for over five hours, from 4:45 to 10:00 p.m. Tornado warnings are much more precise and indicate exactly where and when a tornado is likely to strike. For example, a tornado warning issued by the NWS in Little Rock on February 18, 2000 indicated that a tornado had been detected 10 miles west of Clarendon at 1:32 p.m. This warning advised residents of Keevil that the tornado would arrive at approximately 1:50 p.m.
- The SPC issues a tornado watch when weather forecasters predict there is a possibility of tornadoes. The SPC tags these watches as low, moderate or high, based on the probability that a tornado will occur in the watch area. When there is a strong possibility of violent, destructive tornadoes, the SPC modifies the wording of the tornado watch with the phrase "this is a particularly dangerous situation." You should take all tornado watches seriously and look for updates from your NWS office. Tornado warnings indicate that a tornado has already been spotted in the area, or that the circulation patterns of the thunderstorm could spawn a tornado.
- If the SPC issues a tornado watch for your area, there is no need to panic. Be sure to tune into your local TV or radio station for updates from the NWS office. Go over your emergency plans with your family or colleagues at work. If the NWS issues a tornado warning, take immediate shelter. Go to an interior room on the lowest level of your house. Stay away from windows. If you are stuck outside or if you live in a mobile home, lie face down in a ditch and cover your head with your arms. Try to find a place far from trees or cars.
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