Submitted to Monthly Weather Review

A violent supercell tornado passed through the town of Spencer, SD on the evening of 30 May 1998 producing large gradients in damage severity. The tornado was rated at F4 intensity by damage survey teams. A Doppler On Wheels (DOW) mobile radar followed this tornado, and observed the tornado at ranges between 1.7 km and 8.0 km during various stages of the tornado’s life. DOW3 was deployed less than 4.0 km from the town of Spencer between 0134 UTC and 0145 UTC, and during this time period, the tornado passed through Spencer and peak Doppler velocity measurements exceeded 100 m/s. Data gathered from the DOW during this time period contained high spatial resolution sample volumes of approximately 34x34x37m along with frequent volume updates every 45-50 s. The high resolution Doppler velocity data gathered from low-level elevation scans, when sample volumes are between 20-40 m AGL, are compared to extensive ground and aerial damage surveys performed by the National Weather Service (NWS) and the National Institute of Standards and Technology (NIST). The tornado velocity field is fitted with an axisymmetric vortex to provide a more complete two-dimensional velocity field, which compensates for velocity components perpendicular to the radar beam as well as the translational motion of the tornado vortex