Storm Warning

The NWS has expanded its impact-based warning system to its Central Region to improve communicating the threat of severe weather to the public and emergency agencies. (Photo courtesy of Google)


The cooler-than-normal start to spring might not indicate it, but Minnesota and the St. Croix Valley are heading toward severe weather season and with it comes a new National Weather Service program to better communicate the dangers from approaching storms.

The NWS Central Region, which includes Minnesota, will expand impact-based warnings to all NWS offices. The NWS goal is providing more information to the public, media and emergency management officials, better public response and decision-making and to better meet the public’s needs in the most life-threatening weather events.

Impact-based warnings contain “event tags” at the bottom of each severe thunderstorm or tornado warning which contain more specific threat information to quickly provide persons and organizations with potential high impact risk signals to prompt faster assessment and protective actions.

Impact-based warnings are the result of the more than 550 tornado-related fatalities in 2011 in the U.S. The May 22, 2011, tornado in Joplin, Mo., accounted for 158 deaths, making it the deadliest single tornado since modern record-keeping began in 1950.

The NWS conducted an assessment following the Joplin tornado evaluating weather service warnings and people’s responses. Key assessment findings included:

  • The majority of people said local outdoor warning systems were their first source of alerts;
  • A majority of people then sought confirmation of the threat from additional sources before seeking shelter, and
  • Credible, extraordinary risk signals prompt people to take protective actions.

Impact-based warnings are designed to provide critical information, prioritize warnings and highlight a particularly dangerous storm.

Tornado Tags
Tornado Radar Indicated: Evidence on radar and near storm environment is supportive, but no confirmation.
Tornado Observed: Tornado confirmed by spotters, law enforcement, debris ball signature.

Tornado Damage Threat Tag
Tornado Damage Threat Considerable: When there is credible evidence that a tornado, capable of producing considerable damage, is imminent or ongoing.
Tornado Damage Threat Catastrophic:When 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.

Tornado Tags for Severe Thunderstorm Warnings

Tornado Possible: A severe thunderstorm has some potential for producing a tornado although forecaster confidence is not high enough to issue a tornado warning.