On February 28, 1997, about 1901 central standard time, a Cessna 172P, N98991, registered to Civil Air Patrol Inc., operating as a 14 CFR Part 91 (other work) flight, collided with a pole while taxing. Instrument meteorological conditions (reduced visibility due to rain and ground fog) were reported by the pilot, and an IFR flight plan was filed. The airplane sustained substantial damage. The commercial pilot sustained serious injuries, and the passenger reported minor injuries. The flight originated from Nashville, Tennessee, about 1 hour 35 minutes before the accident. The pilot stated he diverted to Jackson, Tennessee, due to weather. After landing rollout on runway 20, he transitioned to the taxiway to go to the local fixed base operator (FBO). He did not look at the airport diagram due to being familiar with the airport. A heavy rain shower came in from the west and there was some areas of ground fog, which reduced his visibility. He continued to taxi following the yellow line; however, his taxi speed was too fast for the weather conditions that existed, and he did not request any assistance from the flight service station. He taxied onto the ramp, and was looking outside the airplane for the FBO when his passenger said something. He realized the airplane had traveled off the ramp and was on the grass. The airplane collided with a pole before he could apply brakes. When asked what caused the accident, the pilot stated he should have stopped taxiing. He failed to maintain a visual lookout, while trying to locate the FBO and collided with the pole. Review of weather information obtained from Jackson, Tennessee, for the time period of the accident revealed no recorded record of rain or ground fog.