Increased population and urbanization in Syria and other Mediterranean countries is increasing demands on limited renewable water resources. Wheat is a staple crop that is commonly grown in the winter to take advantage of seasonal rainfall. Under good management, supplemental irrigation (SI), either full or deficit, increases and stabilizes yields while also using irrigation water efficiently. However farmers in Syria, like their counterparts worldwide, tend to apply too much water to minimize the risk of applying too little. We sought to develop a model that is useful as a tool to help with scheduling SI. We based our model on the widely available spreadsheet model for full irrigation scheduling presented in FAO publication 56 (FAO-56). The adaptations we made account for limited root growth when rainfall limits soil water zone content, and for the storage of soil moisture below the developing root zone when infiltrated rainwater exceeds current root zone storage capacity. We tested our model with data from Tel Hadya in N. Syria, where average annual rainfall is 350 mm and the soil is deep clay. We used daily weather data from the 1992/93, 1993/94, 1994/95 and 1995/96 seasons and compared predicted soil water within a 1.2m root zone with periodic measurements made with a neutron probe. The mean absolute error in predicted soil water content over this period was 23mm. Although our model remains simple, it performed satisfactorily and has potential for use as an irrigation decision support tool at the farm and strategic levels. The model is initially being used to assist farmers in Al-Ajaz with irrigation decisions.