How Likely Is That Chance Of Thunderstorms? A Study Of How National Weather Service Forecast Offices Use Words Of Estimative Probability And What They Mean To The Public

One of the challenges when communicating forecast information to the public is properly contextualizing uncertainty. No forecast is ever certain, as no meteorological phenomenon is guaranteed to occur. As such, the uncertainty in forecast information should be communicated in a way that makes sense to end users. Previous studies of the communication of probabilistic information suggest that, although the general public are more apt to communicate uncertainty with words of estimative probability (WEPs), they prefer to receive uncertainty information numerically. Other work has suggested that a combination of numbers and WEPs is the best method for communicating probability, but fewer research studies have assessed the communication and interpretation of probabilistic meteorological information. In this study, we code 8900 tweets from the National Weather Service Weather Forecast Offices (WFOs) and analyze them to find how forecasters communicate probabilistic forecast information to the public via Twitter. This analysis reveals that WFO messaging is dominated by WEPs, with few numerical descriptions of probability. These WEPs are generally vague, unqualified notions of probability that may impede the public's ability to interpret the information that forecasters are trying to communicate. Based on this analysis, two publicly fielded surveys also are analyzed in order to understand how participants tend to interpret the most common qualified and unqualified WEPs that WFOs used on Twitter. Though participants generally interpret qualified WEPs more consistently than unqualified WEPs, both categories featured a wide range of interpretations that suggest both types of WEPs are vaguely defined for the general public.