THE PILOT SAID HE ENCOUNTERED ROUGH AIR WHILE ON FINAL APPROACH, 'ALMOST LIKE WIND SHEAR,' BUT HE WAS ABLE TO MAINTAIN CONTROL OF THE AIRPLANE. THE AIRPLANE TOUCHED DOWN, ROLLED A SHORT DISTANCE, THEN NOSED OVER. THE PILOT THEN DISCOVERED THE RUNWAY WAS COVERED WITH SEVEN TO EIGHT INCHES OF 'VERY WET, HEAVY, AND CRUSTY' SNOW.