In an effort to better communicate the imminent danger of powerful thunderstorms and severe weather events, including tornadoes, the National Weather Service (NWS) began issuing experimental, impact-based warning communications in 2012.
Due to the positive feedback, the NWS has expanded the program to include 19 Southern region offices for the spring of 2015.
"Our goal is to better communicate threats to partners and constituents," NWS Severe Storms Leader John Ferree said.
All tornado warnings will include bullets that clearly communicate the hazard and impact information, employ enhanced calls to action and add "tags" at the end of the message with additional critical information, he added.
This information may include whether the tornado is observed or radar-indicated, predicted hail size and the option to add strength of non-tornadic thunderstorm-related wind.
"When there is substantial evidence of a tornado coincident with a high impact event, the phrase ‘This is a Particularly Dangerous Situation' (PDS) will be utilized," he said.
This will also be used along with enhanced wording within the second warning bullet to identify a high level of risk, describe expected damage and impacts and promote serious urgency in taking action to seek shelter immediately, according to Ferree.
In extremely rare cases in which a known violent tornado is likely to produce devastating damage, the enhanced wording will include a "TORNADO EMERGENCY" announcement.
"The recommended action will be brief, clear and extremely urgent," Ferree said.
Examples include the phrases "IF YOU ARE IN OR NEAR (TOWN NAME)...SEEK SHELTER IMMEDIATELY!", and the tag line will read, "TORNADO DAMAGE THREAT...CATASTROPHIC."
"In summary, forecasters will add some clarification to the level of threat of tornadoes and severe thunderstorms based on the level of severity," Ferree said.
The impact-based warnings for tornado warnings, severe thunderstorm warnings and severe weather statements were first tested at five of the National Weather Service's Central Region offices in 2012.
Following the success of the experimental warning product, all 38 Central Region offices were added in 2013, and eight more offices were added in 2014.
"We have had two social science studies that have indicated that Impact Based Warnings had a positive impact on the users in the studies," Ferree said.
"We are awaiting the recommendations from a third social science study that has just begun and will be completed this fall to determine how best to implement this nationwide."
According to Ferree, several NOAA Service Assessments show that confidence and even the body language of broadcasters and other communicators help encourage a proper response from the public during a severe weather event.
"If NWS forecasters can easily communicate confidence that a high impact event is imminent or ongoing, that will help broadcasters, emergency management and other key partners pass along that message," he said.
While the experimental impact-based warning product is limited to tornado warnings, severe thunderstorm warnings and their follow-up statements, Ferree said they must operate under tight restrictions and procedural limitations, which will not drastically alter the existing methods of watches and warnings currently issued by the NWS.
"Any radical change would demand a rather large adjustment by core customers and partners and a massive public education effort," he said. "Therefore, this works within the boundaries of the well-established mass communication channels."
In addition to the NWS's new communications, the National Severe Storms Laboratory has also started a project that will allow forecasters to improve upon standard weather watches and warnings by delivering detailed information as it becomes available.
The project has been named Forecasting a Continuum of Environmental Threats, or FACETS.