A distributed autowave model of the Portevin-Le Chatelier effect has been developed for the region of medium and elevated temperatures in alloys. The model was converted into dimensionless form and the mechanisms of serrated deformation and localization of plastic flow were studied using analytical and numerical approaches. An instability region is found for the rate of plastic deformation and temperature, in the vicinity of which the Portevin-Le Chatelier effect is realized. The critical dimensionless parameters responsible for the variety of spatial-wave solutions of the initial system of equations are determined: the shapes of the load oscillations representing a quasi-periodic sequence of oscillating wave packets; bursts of plastic deformation velocity. The bursts are strictly correlated and form distinct Portevin-Le Chatelier bands under the stochastic deformation regime. Portevin-Le Chatelier bands extend from one end of the crystal to the other, where the reverse band is formed. This process of propagation of deformation bands is periodically repeated.