The Art of Severe Weather Probability: Unraveling the Conditional Intensity Puzzle

Since 1973, the Storm Prediction Center (SPC) has used the Convective Outlook to illustrate the threat of severe weather to a variety of expert to non-expert users. The outlook translates the probability of different hazards (tornadoes, wind, and hail) within 25 miles of a point into a 5-tiered categorical risk scale. This study focuses on a potential change to the outlook: the inclusion of conditional intensity information. Currently, the use of “hatching” in the convective outlook indicates a 10% or greater chance of an EF2+ tornado, 2+ inch diameter hail, or 65+ knot wind gusts expected within 25 miles of a point. In a potential new paradigm, conditional intensity information could be used to indicate when and where significant severe weather reports are more likely to occur within the overall risk area, especially on days when the overall threat of severe weather is low but the potential for significant reports is high. This research will work towards accomplishing several key objectives, including (1) understanding the most effective ways to visualize and communicate conditional intensity information; and (2) investigating whether conditional intensity information will help with decision making. Initial results reveal differences in the way that emergency managers and members of the public interpret conditional intensity information. Moreover, specific changes to the design of this product may increase the user's understanding of conditional intensity, enabling future Convective Outlooks to more effectively communicate the potential intensity of severe weather to the public.