We reported the observation of a mesospheric front with the properties of an undular bore by an OH imager, over the Fort Collins/Platteville area on 6/7 October 2002. Unlike the earlier bore observations, a Na lidar capable of measuring mesopause region temperature, zonal, and meridional winds was in operation concurrently. The lidar data confirm, for the first time, the existence of a collocated temperature inversion layer to serve as the ducting region for bore propagation, as required by the simple theory proposed by Dewan and Picard 6 years ago. In addition, the lidar data in principle provide sufficient information for the determination of all parameters of the bore as suggested by the simple theory. The parameters so determined are compared to two bores previously studied. Like the earlier cases, the horizontal wavelength estimated from the theory is in good agreement with the observation. The lifetime of this undular bore, ~120 min, was considerably shorter than the other two. Continued lidar observation after the bore event reveals that the ducting region may be controlled by a long-period wave, most likely related to a semidiurnal tide, and that atmospheric dynamic instability occurs simultaneously with the destruction of the wave train associated with the bore. It is possible that this constitutes, for the first time, the observation of the transition from an undular to a turbulent, or foaming, internal bore predicted by the theory.