Tornado warning services for misoscale circulations in quasilinear convective systems

Although long known to exist, misoscale circulations in quasilinear convective systems are becoming more readily observable in warning environments due to the improved availability of real-time radar data at higher spatial and temporal resolutions. These circulations are frequently associated with narrow paths of enhanced wind damage, particularly when combined with a fast system motion.

Some of these circulations have been observed to grow in size and/or intensity, and some last longer than others. It is a significant challenge to anticipate in real-time where circulations might develop along the line, which nascent circulations might intensify enough to produce swaths of enhanced wind damage, and which circulations will quickly dissipate.

In a storm environment capable of producing significant misoscale circulations, this presents a major dilemma regarding Tornado Warning services. Large, long duration Tornado Warnings to cover all possible tornadic circulations in a quasilinear system have potentially negative societal implications, setting into motion widespread protective and emergency response actions for, at the most, very isolated impacts. On the other hand, while a few of these circulations might intensify enough to be classified as tornadoes, by the time one is detected and a warning disseminated, the threat is usually over.

This presentation will show archived examples of misoscale circulations in quasilinear convective systems of various sizes, durations, and intensities, to illustrate the wide range of events observed. The discussion will focus on the difficulty in classifying these events as tornadic vs. non-tornadic, the challenge in anticipating transient tornadic circulations among the many weaker circulations, and the dilemma facing forecasters when deciding whether to issue a Tornado Warning during these events. The presentation will conclude with recommendations for effective warning services during such events.