NWS Lincoln to issue enhanced severe weather warnings beginning April 1

Enhanced wording to highlight dangers in severe weather warnings

[March 21, 2013]  The United States was ravaged by tornadoes two years ago. Record numbers of tornadoes occurred in many areas of the country -- and several of them were deadly. More than 550 people were killed by tornadoes, including 158 in Joplin, Mo., alone. Nearly all of the deadly tornadoes in 2011 were preceded by tornado warnings from the National Weather Service -- some with 20 to 30 minutes of advance notice or more. However, the death tolls were extremely high, despite warnings being issued through multiple communications methods.

To address various questions and findings in the wake of the Joplin tornado, the National Weather Service offices in Kansas and Missouri experimented with enhancing severe weather warnings in 2012. The 2012 experiment yielded some successful results; however, due to widespread drought, there were a limited number of cases. The decision was made to expand this experiment to all the weather service offices in its Central Region of the United States -- including the office in Lincoln -- starting April 1.

The "enhanced" severe weather warnings -- or impact-based warnings -- are intended to provide more information about the severe weather threat to the public, emergency managers who activate outdoor warning sirens, and the broadcast media. Tornado and severe thunderstorm warnings from the National Weather Service will look similar; however, the information will be streamlined, including the addition of a new "Impacts" section. That portion of the warning is intended to describe what type of damage can be expected from the warned storm.

The intended outcomes of providing extra information in the impact-based warnings are to improve communication of critical information by the National Weather Service, to make warnings easier to read, to identify the most important information, to highlight storms that are particularly dangerous, to provide different levels of potential storm impacts within the same product, and to enable people to prioritize warnings in or near their areas of interest.

The impact-based tornado warnings will be sent from the National Weather Service in the same manner as in the past, so no changes are needed to weather alert radios or computers and mobile devices programmed to receive these messages. The information within the warning, though, will look and sound a bit different.

With respect to tornado warnings, there are three possible impacts that will be communicated:

• Tornado damage is possible within the area of the warning. In this case, the duration of the tornado is generally expected to be short-lived. (Based on the tornado climatology of central and eastern Illinois, nearly 75 to 80 percent of our tornado warnings will be like this.)

• Credible evidence from trained storm spotters and radar indicates that considerable tornado damage is imminent or ongoing, and the tornado duration is expected to be long-lived. (These are fairly rare in central and eastern Illinois, occurring with about 20 percent of our tornadoes.)

• Catastrophic damage from a tornado is occurring, there is a severe threat to human life, and the tornado duration is expected to be long-lived. This will be exceedingly rare -- and used only when reliable sources confirm a violent tornado. (This type of tornado has occurred only eight times in central and eastern Illinois in the past 63 years and is very rare.)

In addition, severe thunderstorm warnings will be enhanced in the impact-based warnings experiment. With many severe thunderstorm warnings, the primary threat is damaging straight-line wind, severe wind from a downburst or very large hail. However, sometimes, short-lived tornadoes can rapidly develop and cause enhanced damage within an area of high wind. In this case, the severe thunderstorm warning will indicate that there is some potential for a short-lived tornado by stating a tornado is "possible." This will be used when the available radar and storm spotter information does not indicate a widespread, long track tornado threat, and if a brief tornado touchdown may occur.

For more information about the impact-based warnings, visit http://www.crh.noaa.gov/
crh/?n=2013_ibw_info.

The mission of the National Weather Service is to provide weather, hydrologic and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and property and to enhance the national economy. The National Weather Service is the sole United States' official voice for issuing warnings during life-threatening weather situations.

[Text from National Weather Service, Lincoln office]