Monday, April 1, 2013

2013 Thunderstorm Season - "Impact Based" Tornado Warnings Experiment

The NWS Central Region states and offices participating
April 1st marks the start of the thunderstorm season in the central U.S. This year 38 National Weather Service offices in 14 states that comprise the NWS Central Region will be issuing tornado warnings using enhanced messaging to emphasize the particular nature and danger of a storm. These "impact based warnings" (IBW) are an experiment to better communicate the expected impact and damage from a tornado in order to provide additional information to the media and emergency managers and better motivate people to take appropriate action.

This experiment was developed after an assessment of the May 2011 tornado that devastated Joplin, Missouri killing 158 people. There were three key findings from this assessment:
  • The majority of people identified local outdoor warning systems as their first source of warning.
  • The majority of people sought confirmation from additional sources before seeking shelter.
  • Credible, extraordinary risk signals prompt people to take protective actions. 

A number of "tornado tags" will be utilized for tornado.  Two tags will indicate whether the tornado was detected by radar or observed by spotters or law enforcement. Damage threat tags will be used to convey the level of damage expected from a particular storm.  Warnings will include the particular hazard (tornado, hail), the source of the information (spotter confirmation, on-going damage), and the impact and type of damage expected.

The IBW tags allow the forecasters to distinguish between a low-impact event (for example a weak, short-lived tornado) and a high impact event (a large, long-lived tornado)  Large, damaging tornadoes are relatively infrequent, so most of us will never hear a warning for a tornado causing considerable or significant damage.

In 2012 NWS offices in Kansas and Missouri utilized the impact based warnings. Below is a warning issued last year using the enhanced wording. The changes from a "standard" warning are highlighted in red.
Tornado warning issued on April 14, 2012 for central Kansas.

At the conclusion of this storm season the IBW experiment will be independently evaluated to determine its effectiveness.

Will changes in wording actually make a difference? This is an experiment to find out. Public response to warnings is a complicated issue and something that the NWS and emergency officials have wrestled with for years. How the information is communicated (sirens, the broadcast media, the Internet) and the content of the message that is being communicated are two sides of the same coin.

You can read more about the Impact Based Warnings experimental product at this NWS Central Region page.

More background on what was learned from the 2011 Joplin tornado can be found at NWS Central Region Service Assessment Joplin, Missouri, Tornado–May 22, 2011 


  1. I think this is a GREAT plan. For people who are not interested in the weather and who do not know days ahead of time that severe weather is expected, spelling the watches/warnings out in unmistakable language will be very helpful!

  2. I hope it has an effect, but it remains to be seen, Kelly. The is some debate in the meteorological community on how effective this will be. People tend to react according to their past experiences. If they have never been hit be a severe storm or tornado despite being warned (perhaps they are very lucky), will a change in wording be enough to motivate someone to take action?

  3. I do have hope that more clearly defining watches/warnings for people will be a step in the right direction but you are right - there are some who will continue to take their chances!