Understanding the Potential for Public Misinterpretation of Forecast Information: SAWTI and the "Purple Flag Warning"

The Santa Ana Wildfire Threat Index (SAWTI) is a tool used by meteorologists and fire agency managers to categorize Santa Ana wind events with respect to anticipated fire potential. The SAWTI has four threat levels: marginal (yellow), moderate (orange), high (red), and extreme (purple). On December 6^th, 2017, the threat was registered for the first time in purple given expectation of winds reaching 80mph, implying “extreme” fire growth potential. Following a CalFIRE tweet of the SAWTI in purple that morning, the notion of a “Purple Flag Warning” soon developed in the public imagination, appearing in various social and news media over the next eight days. Yet, no such nomenclature exists formally. Here we trace the evolution of the “Purple Flag Warning” in the public imagination during those eight days; noting, from where the language emerged and how it spread, and how quickly it was ascribed a definition then used to interpret certain tactical decisions made by fire agencies. Findings highlight the potential for public misinterpretation of climate and climate-related forecast and warning communication, underlining the accompanying need for heightened clarity in the same.