A technique to extract wind field derivatives and storm characteristic indices from data acquired by a single Doppler radar is described. The technique was applied to four extratropical cyclones observed in Massachusetts. Storm intensity indices that have worked well in tropical cyclones did not perform as well with the extratropical cyclones. The differences of structure between extratropical and tropical cyclones is mainly responsible for the poor performance of the indices. It is possible that when a network of Doppler radars is deployed a comparative analysis to the wind field derivatives and their indices would provide useful forecasting information.