Our main job at the National Weather Service is to issue watches, warnings and other information to help keep you safe when hazardous weather threatens. Your best defense against dangerous storms is to have a plan of action, and to pay close attention to local weather information.
Your chances of receiving a severe weather warning depend on where you are, what you're doing and the time of day the warning is issued. If you are at home watching local television, and have a weather radio, chances are you will know severe weather is headed your way. If you sleeping, traveling, shopping, working, attending a sporting event or other outdoor event, not watching local television or otherwise not paying attention to your local weather, you may not ever receive the warning.
A single warning could turn out to be the most important warning in your life. Knowing how to get information and having multiple ways to hear a warning can help increase the chances you'll hear the warning when it matters most.
The National Weather Service's main job is to issue warnings and other weather information service to help protect life and property. It's important to understand the different types of information available to be able to take full advantage of these critical weather information services. The table below briefly explains the three primary ways we have to inform you about upcoming severe weather - outlooks, watches and warnings.
|Service||What It Means||You Should...|
|Hazardous Weather Outlook||Will there be severe thunderstorms or tornadoes today or tonight, or several days from now?||If severe weather is expected, check back for later forecasts, information and possible watches.|
|Tornado or Severe Thunderstorm Watch||There's a good chance of large hail, damaging winds, and maybe even a tornado in the watch area within the next few hours.||If the watch includes your county, or one close to you, you should really start to pay attention to what's going on. If there are storms nearby, check your weather source to see if there are warnings.|
|Severe Thunderstorm Warning||A storm with large damaging hail and/or damaging winds has been seen, or indicated on radar.||Listen closely to the warning - it will tell you what exactly to expect (hail size and wind speed).|
|Tornado Warning||A tornado has either been seen, or there are signs on radar that a tornado could be forming.||If you're in the warning area, NOW is the time to put your safety plan into action.|
Hazardous Weather Outlooks are designed to give you information on any hazardous weather that is expected over the next seven days. This includes severe thunderstorms and tornadoes. Below is a depiction of what is contained in the Hazardous Weather Outlook, and where to find it in the product.
The current Hazardous Weather Outlook can be found here.
For severe thunderstorm outlooks, NWS Norman characterizes the risk as "slight," "moderate," or "high." The risk category may be an indicator of the expected coverage/number of storms and/or the expected intensity of the storms. Slight risks are quite common in this part of the world, but should not be ignored. It's important to remember that a slight risk does not mean the storms will only be slightly severe. Significant storms can occur in a slight risk area, or in an area that was not even in an outlook early in the day. A slight risk outlook in or near your area should be monitored closely for later changes.
Watches may be issued hours before a storm. The sky may be sunny when you first hear a tornado or severe thunderstorm watch. Remember a watch just means that conditions are favorable for severe thunderstorms and/or tornadoes.
Tornadoes sometimes happen in severe thunderstorm watches. Don't ignore these watches. Remember it only takes one storm or one tornado to make the event significant to you.
Watches can help you get ready for severe storms. Remember that severe storms can occur before a watch is issued.
You should pay attention to where the watch is and how it is oriented. The sky may be blue outside when you first see the watch.
Just because you are on the edge of the watch area does not mean you will not see a severe storm. Storms do not recognize political boundaries such as city limits or county lines, and they can develop or move into areas that are not under a watch or warning.
Do not ignore severe thunderstorm warnings! Severe thunderstorm warnings often precede tornado warnings, providing you with extra time to prepare for a dangerous storm. If there's a severe thunderstorm headed your way, you should monitor it closely, especially if a tornado watch is also in effect.
In addition, severe thunderstorm warnings issued by the NWS in Old Hickory will almost always contain details about the expected hail size and wind speeds.
Often TV stations will display the counties affected by different types of warnings with color coded maps showing tornado and severe thunderstorm warnings. If your county is shown as being in a severe thunderstorm warning, you should try to get more detailed information as to what the storm is capable of doing.
Keep in mind that even without producing a tornado, severe thunderstorms can be violent, dangerous and even deadly events. Severe thunderstorms can produce destructive hail - ranging in size from dime to softballs or larger - winds in excess of 100 miles an hour, flooding rains and deadly lightning.
Tornado warnings cannot be issued for every single tornado that occurs. This is why you must take responsibility for your personal safety any time storms threaten. Do not wait until you get an official warning, either through television, weather radio, or an outdoor warning siren. If you feel threatened, you should take your tornado precautions. It is better to be safe than sorry.
Small and usually weak tornadoes can develop very quickly from any thunderstorm, so always be cautious and alert any time storms are in the area.
National Weather Service tornado warning lead times (the amount of time between when the warning is issued and when the tornado strikes) have shown a steady increase over recent years, and there have been instances where tornado warnings were issued tens of minutes before a tornado struck. However, given the state of tornado forecasting science and knowledge, you will not receive a long advance notice of every tornado. Your safety plans should account for this, and may require that you have an alternate plan for situations when you cannot reach your primary shelter area.
Tornado warnings contain information that lists the cities and towns in the path of a tornado. While your National Weather Service strives to provide the most detailed and accurate information possible, there may be occasions when your small town or community is in the path of a dangerous storm, but is not listed in the warning text. This also holds true for television path forecasts. You should be cautious when using detailed forecasts of time and location. Because of the way radar works and how storms behave, these times and locations could be off by several minutes and several miles. Allow yourself plenty of time to get to your tornado shelter.
Severe weather statements are issued to update warnings, and include new information about an ongoing severe storm. Here is a possible scenario...
5:05 PM A Severe Thunderstorm Warning is issued. The storm is producing golfball size hail.
5:15 PM A Severe Weather Statement is issued to update the warning. The storm is producing baseball size hail and is also showing signs of rotation. A tornado warning might become necessary.
5:20 PM A Tornado Warning is issued.
If you've been paying attention to the entire suite of severe weather products from the National Weather Service, you got an extra 20 minutes notice that a dangerous storm was nearby. If you only pay attention to the tornado warning, this means you got less information and less advance notice. National Weather Service forecasters work hard during an event to keep you informed with a continuous flow of information, from days before the storms develop to reporting the aftermath of the storms.