On September 12, 1999, about 0645 hours Pacific daylight time, a Cessna 182J, N3348F, sustained substantial damage when it collided with trees while maneuvering to land at the McBeth Airport, Klamath, California. The airplane was owned and operated by the private pilot under the provisions of 14 CFR Part 91. The pilot sustained minor injuries and his passenger was not injured. The personal flight departed Napa, California, about 0445. Instrument meteorological conditions prevailed and no flight plan was filed. The pilot stated he received a weather briefing from a Federal Aviation Administration (FAA) Flight Service Station about 2100 on September 11. About 2130 on the September 11, a friend at Klamath told him the weather was clear and there had been no fog for the last couple of days. He departed and cruised en route to Klamath at 10,500 feet, and descended to 1,500 feet once at the destination. He could not spot the airport due to a fog layer, which extended approximately 2 miles up the Klamath River beyond the airport. He flew to the edge of the fog bank and stated it appeared to be from the ground up to 500 feet. He decided to divert to his alternate, Happy Camp, bearing 39 degrees at 32 miles and 1,209 feet. Just after turning toward the alternate airport, the engine began to run rough; the pilot turned the carburetor heat on, switched fuel tanks, leaned the engine, and completed a magneto check. The engine continued to run rough at a power level insufficient for flight, and he was unable to arrest the airplane's descent. He had a global positioning satellite (GPS) unit indicating the Klamath airport's location and turned toward that indication. He was at 500 feet at the top of the fog layer, saw the numbers 29 through the fog, and turned back to the runway. During the turn, he went into the fog. The pilot said the next things he could see were trees. Two trees were taller than the rest and he was headed straight for one of them. He turned to the right to go between the trees just prior to the tree collision. The pilot stated the airplane stopped on top of one of the trees with the nose pointing up. Then the nose slowly went straight down. He braced for impact with the ground, but there was none. The tail lodged in branches and the airplane stopped with the nose about 5 feet from the ground. The right side door was lowest to the ground but jammed. Then he noticed fire in the floorboard area, exited through the pilot's door, and jumped to the ground. The airplane was consumed by the postcrash fire. Witnesses on the ground heard the airplane circle the area twice at a very low altitude, but did not hear any change of engine sound. A METAR (Aviation Routine Weather Report) was issued at 0655 for McNamara Field, Crescent City, California. At an elevation of 57 feet, Crescent City was 19 miles on a magnetic bearing of 307 degrees from Klamath, which has an elevation of 42 feet. It reported a temperature of 10 degrees Celsius and a dew point of 8 degrees. According to a carburetor icing probability chart in the FAA publication, "Tips on Winter Flying," the accident temperature/dew point conditions were conducive for serious carburetor icing at cruise or climb power. The publication stated, "Partial throttle (cruise or letdown) is the most critical time for carburetor ice . . . It is recommended that carburetor heat be applied before reducing power."