WHILE LANDING HIS ACFT AT BASSETT, NEBRASKA THE PLT RPTD A GUST OF WIND HIT THE ACFT FM BEHIND AND HE LOST DIRECTIONAL CONTROL VEERING OFF INTO A SNOW BANK. THE PLT STATED THAT TWO WITNESSES WHO WERE WALKING NEAR THE RWY TOLD HIM NO WIND WAS BLOWING WHEN THE ACFT FIRST TOUCHED DOWN ON THE RWY. AFTER TOUCHING DOWN ON THE RWY, THE WITNESSES REPORTED A GUST OF WIND STRUCK THE REAR OF THE ACFT. WIND OBSERVATIONS OBTAINED FM THE NATIONAL WEATHER SERVICE OBSERVER LOCATED IN AINSWORTH, NEBRASKA 19 N.M. WEST OF BASSETT SHOWED WINDS FM 290 DEG. AT 15 KTS AT THE TIME OF THE ACCIDENT. THE PLT CHOSE TO LAND ON RWY 13 AFTER SEEING THE WINDSOCK HANGING DOWN. THE WITNESSES STATED THE WIND HAD BEEN BLOWING ERRATICALLY MOST OF THE DAY, POSSIBLY GIVING THE PLT A FALSE INDICATION OF WND CONDITIONS. THE ARPT TETRAHEDRON, ANOTHER SOURCE OF WND DIRECTION, SHOWED THE WND WAS BLOWING FM THE NW MAKING A LANDING TO RWY 31 THE APPROPRIATE CHOICE.