What is already known:
What this study adds:
Uncertainty is inherent in every weather forecast. In order to create better methods to communicate uncertainty to the public and other end users, it is necessary to understand how forecasters think about and understand it. Around twenty hours of observational data from the National Oceanic and Atmospheric Administration (NOAA) Hazardous Weather Tested Spring Experiment (HWT) 2012 was collected in order to analyze the participants’ assessment of uncertainty in a real forecasting environment. Also, ten in-depth interviews were carried out in which research and operational forecasters were asked several questions regarding uncertainty. The interviews were recorded and transcribed for analytical purposes. Results show that even though the forecasters in this study were aware of the inherent uncertainty in severe weather, they were unable to quantify it, nor did they have a consensus on its definition. Moreover, the forecasters lacked a conceptual model of uncertainty. Instead, they used their internal climatology as both a tool and a framework to describe and assess uncertainty. Finally, population size was the most important non-meteorological factor that they used to assess spatial uncertainty.