On 27 May 2000, a line of isolated cells over western Missouri propagated eastward along a warm front and subsequently evolved into a tornadic derecho event to the north of St. Louis. The derecho evolved in a highly unstable–moderate shear environment. At least two small, embedded bow echoes and three well-defined low-level radar-detected circulations were observed within the southern part of the convective system. Two of the circulations were tornadic, caused F0 – F1 damage and had path lengths exceeding 10 km. All three circulations exhibited spatial scales typical of tornadocyclones and were difficult to identify in real-time due to their extremely small core diameters.

This paper will present detailed radar and damage analyses illustrating the evolution and relationship between the bow echoes and the small-scale circulations. In particular, two of the low-level circulations, one tornadic and one non-tornadic, formed just south of the merger point between the leading convective line and isolated cells initiated ahead of it. The other tornadic circulation formed just north of a bow echo apex. All circulations were identifiable in radar data and were initially observed below 2 km. All three vortices revealed non-descending characteristics. The implications for real-time detection of these small-scale circulations will also be discussed.