Impact Based Warnings

Impact Based Warnings

The National Weather Service has introduced Impact Based Warnings for tornadoes.


2011 proved to be a historic year in terms of the number of tornado fatalities image of ligtningacross the United States with over 550 fatalities. The May 22, 2011, Joplin tornado resulted in 158 of those, making it the deadliest single tornado since modern record keeping began in 1950. Following the historic Joplin tornado, the National Weather Service (NWS) conducted a service assessment for the purpose of evaluating NWS warnings and societal response to those warnings.

Key Findings from 2011 Joplin 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

Demonstration Project

To address these findings the NWS Central Region will expand to all their offices

the impact based convective warning experimental product to better communicate threats to partners and constituents. The goals in this multi-step process are to provide more information to media and EM partners, to facilitate improved public response and decision making; and to better meet societal needs in the most life-threatening weather events.

Any effort to change core convective warning products must operate under tight restrictions, including time constraints and procedural limitations. In addition, any radical changes to the convective warning products would demand a rather large adjustment by core customers and partners; and a massive public education effort. Therefore, this demonstration will work within the boundaries of the well-established weather enterprise infrastructure to ensure easy absorption into mass communication channels.

Initial efforts will build upon pre-existing Central Region efforts to employ “event tags” at the bottom of each severe thunderstorm and tornado warning. The additional event tags will contain more specific threat information as a quick means to provide users and partners with potential high impact risk signals that prompt faster risk assessment and protective action.

Intended Outcomes

  • Optimize the convective warning system within the existing structure
  • Motivate proper response to warnings by better distinguishing situational urgency
  • Realign the warning message in terms of societal impacts
  • Communicate recommended actions/precautions more concisely
  • Evaluate NWS ability to distinguish between low impact and high impact convective events

The National Weather Service and NOAA have provided this Brochure on Impact Based Warnings. (PDF)

Visit their site to learn more: