Particle Image Velocimetry (PIV) measurements were performed in laboratory-scale experimental fires spreading across horizontal fuel beds composed of aspen (Populus tremuloides Michx) excelsior. The continuous flame, intermittent flame, and thermal plume regions of a fire were investigated. Utilizing a PIV system, instantaneous velocity fields for the three regions were measured and special attention was given to the coherent fluid dynamic structures that are present in a propagating fire environment. Measurements were performed inside the fire itself and in the surrounding environment. From the PIV data the formation of vortex structures in front of the fire were observed. For the 3 flame regions, instantaneous velocity field data was analyzed to determine existing vortex diameters and vorticity values. The presented results of the detailed and measured velocity field within a propagating fire are likely the first of its type.