In this paper we present a theoretical model which permits the conservation equations of fluid dynamics to be conditioned in a fashion analogous to the experimentalist's technique of ‘conditioned sampling’. The detailed analysis refers to the best-known sampling condition, outer-edge intermittency; but the model equation may be applicable to other flow situations, wherein condition- ing exposes details of the physical phenomena. The analysis results in predic- tions of the flow variables within the turbulent flow and of the intermittency. Comparison is made with two sets of experimental results for the two-dimensional mixing layer and with a boundary layer.