Vast majority of Joplin residents did not seek shelter after May 22 tornado warning

(The following is the executive summary of the National Weather Service report on the May 22 Joplin Tornado issued today.)

On May 22, 2011, one of the most devastating tornadoes in the nation‘s history directly killed 159 people and injured over 1,000 in Joplin, Missouri. From a National Weather Service (NWS) perspective, this was essentially a ―warned‖ event in that advance notice of the tornado was given, critical information was communicated and received, and most people sought the best shelter available to them. The timely actions of the ‖weather enterprise‖ (NWS, media, emergency management), and the eventual response of local businesses, churches, schools, and the general public undoubtedly saved many lives.

The NWS Springfield Weather Forecast Office was well prepared and performed in an exemplary manner in both its provision of services and its application of scientific expertise. The professionalism and dedication of the staff members is clearly a credit to the communities they serve.
Still, to learn what more can be done to help reduce fatalities from strong and violent tornadoes, the assessment team examined relevant issues ranging from internal NWS warning operations to dissemination strategies to public warning response. To help accomplish this, nearly 100 interviews were conducted in Joplin with tornado survivors, local businesses, media, emergency management, NWS staff, city officials, and others.

Many of the key findings within this report involved societal aspects of warning response and risk perception. Responding to warnings is not a simple act of stimulus-response, rather it is a non-linear, multi-step, complex process. Relationships between false alarms, public complacency, and warning credibility are highly complex as well.

The vast majority of Joplin residents did not immediately take protective action upon receiving a first indication of risk (usually via the local siren system), regardless of the source of the warning. Most chose to further assess their risk by waiting for, actively seeking, and filtering additional information.

The reasons for doing so were quite varied, but largely depended on an individual‘s ―worldview‖ formed mostly by previous experience with severe weather. Most importantly, the perceived frequency of siren activation in Joplin led the majority of survey participants to become desensitized or complacent to this method of warning. This suggests that initial siren activations in Joplin (and severe weather warnings in general) have lost a degree of credibility for most residents – one of the most valued characteristics for successful risk communication.

Instead, the majority of Joplin residents did not take protective action until processing additional credible confirmation of the threat and its magnitude from a non-routine, extraordinary risk trigger. This was generally achieved in different ways, including physical observation of the
tornado, seeing or hearing confirmation, and urgency of the threat on radio or television, and/or hearing a second, non-routine siren alert.
This report suggests that in order to improve warning response and mitigate user complacency, the NWS should explore evolving the warning system to better support effective decision making. This evolution should utilize a simple, impact-based, tiered information structure that promotes warning credibility and empowers individuals to quickly make appropriate decisions in the face of adverse conditions. Such a system should:

a. provide a non-routine warning mechanism that prompts people to take immediate life-saving action in extreme events like strong and violent tornadoes

b. be impact-based more than phenomenon-based for clarity on risk assessment

c. be compatible with NWS technological, scientific, and operational capabilities

d. be compatible with external local warning systems and emerging mobile communications technology

e. be easily understood and calibrated by the public to facilitate decision making

f. maintain existing ―probability of detection‖ for severe weather events

g. diminish the perception of false alarms and their impacts on credibility
While the weather enterprise was generally successful in communicating the Joplin tornado threat in a timely manner, current communication and delivery mechanisms are not seamless and are somewhat antiquated.

Specifically, many warning dissemination systems are not fully compatible with specific warning information provided by storm-based warning polygons— occasionally resulting in untimely gaps and confusion during dissemination. To improve the warning dissemination system and provide a more coordinated warning message, the NWS should continue to advance the development and cultivate the use of GPS-based mobile communications technologies and Emergency Alert System/NOAA Weather Radio upgrades.

Last, an important impediment to heightening the urgency of the severe weather message from the Weather Forecast Office was the WSR-88D Volume Coverage Pattern strategies available to forecasters. Low level rotational intensification and tornado genesis occurred very rapidly as the storm approached Joplin. Limited scans (every 5 minutes) at the lowest elevations slices likely impacted the WFO ability to quickly ascertain the magnitude of the event. To enhance the ability to monitor rapid tornado genesis, the NWS should develop and implement additional Volume Coverage Pattern strategies that allow for more continuous sampling near the surface (e.g., 1-minute lowest elevation sampling).

The complete report can be found at this link.