On August 15, 1997, approximately 1105 mountain daylight time, a Waco KNF, NC698N, was substantially damaged when it collided with terrain during a precautionary landing near Wamsutter, Wyoming. The commercial pilot, the only occupant aboard, was not injured. Visual meteorological conditions prevailed, and a VFR flight plan had been filed. The flight originated at Rawlins, Wyoming, approximately 1000. In his accident report, the pilot said he was about 5 to 10 miles west of Rawlins when he experienced "a lifting action (desert wave). . .holding (a constant) altitude produced an indicated airspeed of about 10 knots higher than normal and required a power reduction to avoid engine overspeed." As the pilot approached Wamsutter, he encountered "an opposite wind effect. . .(with) full power RPM and holding climb speed resulted in a very slow descent." When the airplane continued descending below 200 feet agl (above ground level), the pilot chose to make a precautionary landing on a gravel road. The pilot made a wheel landing but a wind gust caused the airplane to become airborne again. As the airplane settled back to the ground, "a really weird and severe (wind) gust lifted the right wing beyond any amount of aileron control (clear to the stop) and pitched the plane nose down into a ditch alongside the road)," where it nosed over. Weather documents used by Casper, Wyoming, Flight Service Station (FSS) personnel to brief the pilot were submitted for review. The Rock Springs area forecast (TAF), issued at 1142 and valid for a 24-hour period beginning at 1200, indicated the wind would be from 270 degrees at 25 knots, with gusts to 37 knots. The Rawlins area forecast, covering the same time period, indicated the wind would be from 230 degrees at 22 knots, with gusts to 32 knots. AIRMET (Airman's Meteorological Information) Tango update 2, issued at 0745 and valid until 1400, predicted occasional moderate turbulence below FL (flight level) 180 (18,000 feet) due to moderate northwesterly winds. The airplane's true indicated airspeed, as filed by the pilot on his VFR flight plan, was 65 knots.