This produces favorable conditions for vortex tube stretching and landspout formation. As time goes forward in figures 5B-C , and the boundaries merge from north to south, new misocyclones reach tornadic strength as they encounter greater low level convergence. In addition, the presence of the westward moving outflow boundary, acting as a density current, suggests that it may have provided additional vorticity as its solenoidal circulation was tilted into the updraft at the boundary intersection. The significance of this mechanism in the landspout spin up process is unknown but it may have played a role in this event's evolution. Summary The evolution of an unusual multiple landspout event has been documented with surface, WSR-88D radar, satellite, and video data.
Observations suggest that landspouts formed as two separate surface boundaries interacted.
The westward moving outflow boundary served to enhance low level convergence as the boundaries collided. This additional convergence likely aided convective growth and the potential for vortex stretching. The angle at which the two boundaries collided allowed for a series of landspouts to develop as each preexisting misocyclone, in-turn, encountered greater forcing. The presence of the westward moving outflow boundary may have also provided additional vertical vorticity as the horizontal vorticity at the leading edge of the boundary was tilted into the vertical. The authors would like to thank Jeff Waldstreicher for his review of the manuscript and his insight during many discussions on this topic.