WINDSHEAR ON LNDG. WINDS ON APCH WERE STRONG AT 4000 FT AND DROPPED DRAMATICALLY AT LOWER ALTS; BUT FLUCTUATING. RPTR HAD 2 RAPID ROLLS BELOW 40 FT; PROBABLY DUE TO XWIND. RPTR ATTRIBUTES TOPOGRAPHY TO UNUSUAL WIND CONDITIONS.

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AFTER FMG (MUSTANG VOR) WE WERE VECTORED FOR THE ILS/DME TO RWY N16R AT RNO. WX CONDITIONS WERE BEING RPTED AS 3000 FT OVCST WITH VISIBILITY OF 10 MI. WINDS HAD PREVIOUSLY BEEN GUSTY BUT WERE NOW FROM THE S AT 8 KTS. DURING THE DSCNT FROM FMG TO INTERCEPTING THE FINAL APCH COURSE; THE RIDE WAS QUITE CHOPPY OVER THE HILLS. ON FINAL PRIOR TO GS INTERCEPT THE WIND WAS FROM THE S 45-50 KTS AT 3000-4000 FT AGL. WE BROKE OUT OF THE CLOUDS ABOUT 2500 FT AGL. THE WIND WAS STILL S AT 45 KTS. AS WE DSNDED DOWN TO 1000 FT AGL THE WIND DROPPED OFF TO ABOUT 17 KTS. THE RIDE WAS STILL CHOPPY AND THE AIRSPD WAS FLUCTUATING +/-5 KTS. THE AUTOTHROTTLES WERE DISCONNECTED AT ABOUT 1500 FT AGL FOR A MORE STABLE RIDE. WIND AT THE SURFACE WAS STILL RPTED AS 8 KTS. THE RWY WAS WET WITH EVIDENCE OF RECENT RAIN. AUTOPLT WAS DISENGAGED BTWN 800-1000 FT AGL. AIRSPD WAS STABLE AND FUEL FLOW ABOUT 4500 LBS WHICH SEEMED APPROPRIATE FOR THE WT; WIND AND DENSITY ALT. AT 50-70 FT AGL; THE ACFT STARTED AN ABRUPT ROLL TO THE L AND JUST AS QUICKLY IT STOPPED. AT 40 FT AGL THE ACFT WAS STABLE ON CTRLINE OVER THE END OF THE RWY AND ON AIRSPD. AT 10 FT AGL THE ACFT STARTED A WING ROLL TO THE R; THAT WAS ABRUPTLY ARRESTED AS THE ACFT TOUCHED DOWN AT ABOUT 1000 FT ON CTRLINE. TOUCHDOWN AND ROLLOUT WERE NORMAL. THE ROLL WAS DRAMATIC ENOUGH FOR THE FO TO SAY 'GAR.' HOWEVER; BY THE TIME HE SAID 'AROUND' THE ACFT WAS ALREADY ON THE RWY. LATER; THE FLT ATTENDANTS ADVISED ME THAT THEY WERE CONCERNED ENOUGH TO MENTALLY REVIEW THEIR EVAC PROCS. NO ACCIDENT; NO INCIDENT BUT NOT ROUTINE. WE COULD ONLY ATTRIBUTE THE SIT TO A RATHER DRAMATIC LOCALIZED WINDSHEAR. PERHAPS; THERE ARE OTHER FACTORS. THE TOPOGRAPHY SURROUNDING THE ARPT MAY HAVE CONTRIBUTED. THE ARPT BEING LOCATED IN A VALLEY WITH AN OPENING AT THE S END THAT COULD POSSIBLY FUNNEL SOUTHERLY WINDS IN SUCH A WAY TO CAUSE UNUSUAL PHENOMENA.