Making History: The First Recorded November Tornado in Idaho (114)

Kurt Buffalo, National Weather Service, Pocatello, ID



On the afternoon of 17 November 2017, a tornado occurred just northeast of the city of Idaho Falls in southeast Idaho. This tornado signifies the first November tornado ever recorded in the state of Idaho. This unprecedented November Idaho tornado occurred in an anomalous environment, characterized by surface temperatures in the 30s (F) and light snow cover on the ground. In this cold environment, the convection from which the tornado developed was producing snow showers rather than rain. The falling snow, along with the light snow on the ground lofted by the circulation, led to a highly visible tornado that quickly caught the attention of many southeast Idaho residents. The tornado was weak and brief, ranking EF-0 on the Enhanced Fujita Scale and lasting on the order of five to ten minutes, but it did produce some minor damage to a rural residence. Perhaps more significantly, its occurrence illustrated that non-mesocyclonic tornadoes can occur in very diverse environments, as long as a few key ingredients exist. This study will take a detailed look at the mesoscale environment -- highlighting both the similarities to, and differences from, more traditional non-mesocyclonic tornado environments. We will show that despite the anomalously cold conditions for a tornadic storm, the mesoscale environment on this day portrayed some similarities to a more typical non-mesocyclonic tornado environment. The identification of these common characteristics in the pre-storm environment could prepare forecasters for the possibility of a non-mesocyclonic tornado in what would otherwise generally appear to be an unfavorable environment. We will also look at whether the complex terrain of southeast Idaho could have played a contributing role in tornadogenesis.