Utilizing Environmental and Radar Predictors to Anticipate Tornado Intensity

Relatively weak tornadoes in the EF0/EF1 category are by far the most common type of tornado, though historically less than 0.5% of such tornadoes have been responsible for deaths. Strong and violent tornadoes in the EF2-EF5 categories have proven much more likely to kill. The anticipated tornado intensity thus would be critically valuable information to include in National Weather Service (NWS) Tornado Warning products. This is true both for weaker tornadoes and those for which the threat is expected to be considerable or catastrophic as per the NWS Impact-Based Warning tags. This presentation shares results from an effort to determine whether the severity of a specific tornado can be anticipated with confidence based on near-storm mesoscale environmental conditions together with Doppler radar reflectivity, velocity, and dual-polarization signatures.

Recent studies using environmental tools such as the Significant Tornado Parameter have suggested it is in fact possible to distinguish environments supportive of strong and violent tornadoes from those more supportive of weaker tornadoes. Studies utilizing radar data also have identified correlations between certain signatures and the strength of the resulting tornado. For example, stronger rotational velocities in a mesocyclone typically equate to stronger tornadoes, as does the presence of a tornadic debris signature at higher levels of a storm. It is less clear how effectively environmental and radar predictors can be utilized together in real-time to support inclusion of anticipated tornado intensity in NWS Warnings.

A key challenge is the fact that environmental parameters and radar signatures both show considerable overlap between values associated with weak tornadoes and those indicative of stronger tornadoes. It can also be difficult to determine the true magnitudes of these parameters in an operational setting. Additionally, the documented severity of a tornado depends greatly on what it happened to strike. Despite these and other challenges, we have sought to establish thresholds for distinguishing EF0/EF1 tornadoes from EF2-EF5 tornadoes for purposes of communicating this information to the public, while not inadvertently downplaying a strong or violent tornado.