The present investigation was undertaken to identify the quantitative relationship between weather parameters and district level yield of cotton and to develop preharvest forecast models for cotton yield. For this purpose 32 years weather and crop yield records of Banaskantha district were collected. It was found that the 26 week crop period model ( using original weather variables, week wise approach) was recommended for pre harvest forecast due to higher R2 value and lower simulated forecast error. The time trend, maximum temperature, morning and evening relative humidity have significantly affected on crop yield.