Probabilistic assessment and prediction of drought provides valuable information for water resources planners and policy makers for developing drought mitigation strategies. In this study an evaluation of drought conditions in northwest of Iran was performed by means of the Joint Deficit Index (JDI). Monthly precipitation data from 1970 to 2007 based on 50 gauge stations uniformly distributed across the area were used for calculating the JDI. Results show that the JDI provides a comprehensive assessment of droughts and that it is capable of reflecting both emerging and prolonged droughts reported in the data. Furthermore, the method provides a basis for determining the amount of precipitation required to reach normal conditions in future months (1–3months examined in this study), and the exceedance probability of this precipitation amount. Performance evaluation based on 6years of independent precipitation data from the region showed Critical Success Index of 0.61 (0.64) for the 1-month (3-month) ahead prediction of the drought conditions. The analysis in this study indicated a good skill in predicting the evolution of drought conditions for the region based on JDI evaluated from monthly precipitation data.