Beyond the Typical Weather Forecast: Harnessing Probabilistic Graphics for Effective Emergency Management

Severe weather is challenging to predict but even more so to decide when to prepare. County Emergency Managers (EMs) and other local officials are tasked with the dilemma regularly of being fiscally prudent yet always prepared. Before the exercise, background interviews were conducted with EMs in two counties in northern California to better understand local concerns and their decision-making processes. Tabletop exercises were then conducted to better understand whether two experimental graphics could better support the difficult decisions being made. During analysis, special attention was given regarding the two probabilistic graphics: a box-and-whisker graph showing 24-hr periods of the model spread of rainfall between the 10th and 90th percentile and a stacked bar graph showing the probability of exceedance for several amounts of rainfall over 24 hr periods. Because each site of the tabletop exercise had a high number of participants, an anonymous online survey about the two graphics helped ensure everyone could provide their input. Surveys and tabletop discussions were analyzed to understand how EMs and other local officials use weather forecasts, particularly how understandable the probabilistic graphics were and whether they would be used prior to a potential flooding event. The results show that both graphs were helpful in the decision-making process. However, many participants need the meteorologist’s interpretation, and many asked for a finer breakdown in time periods showing when the rain would fall to optimize their decisions.