Automotive radar sensors, which fundamentally use millimeter wave signals, increasingly become one of the important comfort and collision mitigation products in the automotive market. Their performance may be affected by wetness due to adverse weather conditions unless proper antenna lens or radome design used, as implemented with the Bosch Long Range Radar System. The extension of automotive radar sensors from comfort to safety systems may further require intelligent features, such as detection of weather phenomena and performance controlling during adverse weather conditions. Hence, this work examines effects of wetness on the millimeter radar performance and methods to identify such phenomena. It reveals that, effects of wetness on millimeter radar has to be generally taken in to account and will provide performance information on automotive radar sensors. The information is used for controlling automotive radar sensor performance, which makes it more intelligent and robust in adverse weather conditions.