Monday, April 1, 2013

Impact Based Warnings - What does this mean for us?

After one of the deadliest years for tornado fatalities in the United States in 2011, the National Weather Service conducted an assessment of the purpose of tornado warnings issued and societal response to them. That year included one of the largest tornado outbreaks ever recorded in the April 25th - 28th outbreak, as well as the catastrophic EF5 Joplin tornado. The assessment focused on the Joplin tornado, which was the deadliest tornado on record. Part of the problem that the NWS found in this assessment was how the general public received the message of this tornado warning. Most of the residents of Joplin found out about this warning from the outdoor warning systems and before even seeking shelter, these people sought out more information from additional sources. Despite these warnings, it was discovered that the residents of Joplin weren't taking these warnings seriously. So the NWS tried to think of a way to stress importance on future storms that may have similar impacts as the Joplin tornado.

Starting today, the National Weather Service will begin using new Impact Based Warnings in our area. The goal of these new warnings is to provide more information to the media and Emergency Managers, to facilitate improved public response and decision making; and to better meet societal needs in the most life-threatening weather events.

They will use five different tags at the end of a warning to help achieve this.
  • Tornado Possible - Added at the end of a severe thunderstorm warning stating that there is potential for producing a tornado, but the forecaster confidence is not high enough to issue a Tornado Warning.
  • Tornado, Radar Indicated - Evidence on radar and near storm environment is supportive, but no confirmation.
  • Tornado, Observed - Tornado is confirmed by trained spotters, law enforcement, etc.
  • Tornado Damage Threat...Significant - There is credible evidence that a tornado, capable of producing significant damage, is imminent or ongoing.
  • Tornado Damage Threat...Catastrophic - There is a severe threat to human life and catastrophic damage from a tornado is occurring, and will only be used when reliable sources confirm a violent tornado.

On the left is an example of what this new text added to a tornado warning will look like. Notice how this text will highlight what the hazard is, where the source of the information on the tornado is coming from, and what kind of specific impacts that can be expected.

The goal that the National Weather Service has for this is for the general public to use this to help differentiate between low impact and high impact events. The hope is that people will be able to use this extra information to really help keep themselves safe when severe weather strikes.

So we are asking you, what do you think about these new Impact Based Warnings? Will this extra information help you pay attention to particularly dangerous storms or not? Let us know what you think, email us at

Eddie Wildermuth
WTVO Weather Intern

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