At 21:30 CDT, the pilot of a Beech Sundowner was killed when he lost control in severe weather. Witnesses reported IMC prevailed at the time of the accident but there was no flight plan. Two witnesses reported seeing the airplane flying about one mile northeast of the Mandan Municipal Airport during a thunderstorm. One of the witnesses said she saw the airplane pitching up and down and rolling left and right violently before losing sight of it due to very heavy rain. The second witness said the wind was so gusty it almost pushed his car off the road. The airplanes ground impact location was in a field, with vegetation bent almost parallel to the ground about 300 feet around the impact point.