The role of medium-scale interleaving of temperature and salinity in frontal regions is investigated and a model is presented in which a statistical equilibrium of the medium scale is achieved. Small-scale diffusion across intrusions, causing an attenuation of their T/S characteristics, is balanced by horizontal advection of heat and salt by the medium-scale motions. The “energy” source for the balance is the lateral variation in the temperature/salinity field associated with water mass transitions. Estimates of the cross frontal heat or sole exchange can he made based upon the intensity of the interleaving T/S fields. The lateral transfer is directly proportional to the vertical transports across intrusion boundaries by microscale processes. The same general principle for the enhancement of the cross frontal heat transfer by interleaving is similar to that achieved in automobile cooling systems by a radiator. The model, in effect, attempts to quantify our ignorance of lateral mixing of water masses. It is also shown to be a generalized statistical extension of longitudinal dispersion in pipes suggested by Taylor (1953).