Near blowoff dynamics and blowoff characteristics of premixed flames stabilized by a triangular flame holder in the midspan of a rectangular duct were studied using high speed imaging at 500 fps and simultaneous PIV and OH PLIF. Near blowoff dynamics manifested by the onset of asymmetric vortex shedding and local extinction in the form of flame holes were observed. Observations are presented describing the final blowoff event and its precursor: asymmetric sinuous modes of flame motion. It has been hypothesized that partial or total extinction of flame in the shear layers is the major factor that determines the evolution of the asymmetric mode and the final blowoff event. This phenomenon is further evidenced by an observation of the presence of flame kernels within the recirculation zone which under stable conditions contain only combution products. Whether a flame can survive an almost total extinction is governed by the ability of a reacting wake during these times to reignite the extinguished shear layers.