AbstractTo take account of the effect of weather on the cereal harvest, a simulation model is outlined in which rates of combine work, harvest weather, and diurnal grain‐moisture content are regarded as probabilistic, with known distributions based on empirical data. On the basis of this data, the interaction of the variables is assessed over a thousand “years” of synthetic harvesting experience, in which the timeliness of the harvesting operation is assessed in terms of increased grain drying costs, and which is repeated to assess various policies which might be adopted by farmers. The results are presented as normative average total cost curves for various harvesting systems, based on the certainty equivalence of the decision under risk.