Although information about weather forecast uncertainty has been available for some time,it is rarely included in public forecasts and is underused by professional forecasters. The perception is that information about forecast uncertainty is difficult to understand, especially for the general public. Indeed, a large body of psychological research suggests that people have difficulty understanding and reasoning with uncertainty, particularly when it is expressed as probability. What is the impact of uncertainty information on deterministic forecasting? Does ones understanding of forecast uncertainty depend on how it is expressed? Does the display format impact the subsequent decisions? These are some of the questions that were explored in a series of studies investigating the psychological effects of uncertainty information on threshold forecasting decisions.