Flame blowoff under harmonic forcing of upstream mixture velocity is analyzed for bluff-body stabilized conical premixed flames in a laboratory burner. It is found that the forced vortex shedding phenomenon within the recirculation zone, accompanies flame blowoff when the convective wavelength of the imposed oscillation is larger than the recirculation zone length in the streamwise direction. The experimental results obtained from combined particle image velocimetry and planar laser induced fluorescence of OH radical provide evidence for this behavior. The differences between forced and unforced flame blowoff are also discussed. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.