Pilot’s Encounter With Convective Weather Conditions, Which Resulted In A Loss Of Airplane Control Analysis: The airplane was on an instrument flight rules flight and air traffic control (ATC) provided the pilot with vector guidance to avoid an active military operations area (MOA). The controller informed the pilot that he would only be able to deviate to the left of his course due to the active MOA. At that time, the airplane was in an area of developing convective weather activity and likely in instrument meteorological conditions. The pilot reported to ATC that he encountered freezing rain. ATC communications revealed that the pilot requested to deviate to the left of his course due to weather, including mention of encountering freezing rain, which ATC approved.