Perceptions and Reactions to Tornado Warning Polygons: Would a Gradient Polygon be Useful?

To better understand people’s interpretations of National Weather Service’s tornado warning polygons, 145 participants were shown 22 hypothetical scenarios in one of four displays—conventional polygon, conventional polygon + radar image, gradient polygon, and gradient polygon + radar image. Participants judged each polygon’s numerical strike probability (p_s) and reported the likelihood of taking seven different response actions. The conventional polygon display produced p_s that were highest at the polygon’s centroid and declined in all directions from there. The conventional polygon + radar display, the gradient polygon display, and the gradient polygon + radar display produced p_s that were high at the polygon’s centroid and also at its edge nearest the tornadic storm cell. Overall, p_s values were negatively related to resuming normal activities, but positively correlated with expectations of resuming normal activities, seeking information from social sources, seeking shelter, and evacuating by car. These results replicate the finding that participants make more appropriate p_s judgments when polygons are presented in their natural context of radar images than when they are presented in isolation and that gradient displays appear to provide no additional benefit. However, the fact that p_s judgments had moderately positive correlations with both sheltering (a generally appropriate response) and evacuation (a generally inappropriate response) suggests that experiment participants experience the same ambivalence about these two protective actions as people threatened by actual tornadoes.