At 14:30 PDT, a Smith Aerostar 601P suffered structural damage during an encounter with severe turbulence and an in-flight upset near Shoshone. The three occupants were not injured. During the pilots preflight weather briefing, he was advised that AIRMETS for moderate or greater turbulence were in effect for his route of flight. The aircraft was in cruise flight at 14,000 feet when it inadvertently penetrated a thunderstorm. The pilot said that at one point the aircraft was inverted and lost over 8,000 feet of altitude before he was able to regain control.