CHI85LA155

After a practice instrument apch, the plt (PIC) entered the traffic pattern to land on rwy 23. While in the pattern, theair became very turbulent. UNICOM reported the wind was from 270 deg at 20 gusting 35 KTS. On final apch with the flaps fully extended, the plt initiated a go-around at aprx 50 ft AGL & applied power to 36' manifold pressure. He stated thatthe airspeed was aprx 110 KTS when the acft encountered a severe vertical downwind shear, struck the ground aprx 10 ft west of the rwy, & hit a rwy light. Two witnesses noted that the acft appeared so slow on final apch that they went to the UNICOM to advise that 'the winds were now 290 deg at 25 gusting to 35.' They said power was applied & the acft pitched nose down. Also, a witness reported 'heavy' wx aprx 10 to 15 mi west of the arpt, moving east, & rain began shortly after the accident. The flt manual noted: when power is advanced for a go-around from a low power, full flap approach, a nose down pitch will occur which must be countered with aft control input.