The effect of opposing flow on flame spread rate over thin solid fuel is investigated with the help of scaling theory, a comprehensive computational model, and experiments conducted aboard the International Space Station. While spread rate over thin fuels is independent of the opposing flow velocity in the thermal regime, in the microgravity regime, where the opposing flow can be very mild or even completely absent in the absence of buoyancy induced flow, the spread rate is known to decrease as the opposed flow is reduced. Under certain conditions, this can lead to flame extinguishment at a low enough flow velocity. This paper combines scaling arguments with computational results to predict a critical flow velocity for such flame extinction. Results from the recently conducted limited number of space based tests, presented in this paper, seem to confirm the prediction validating the closed-form formula for the critical extinction velocity. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.