AN A320 PILOT REPORTS SEVERE TURB AT FL350 WHERE 5 MINS EARLIER NO ACTIVITY WAS RPTED. ACFT CLBED 1;500 FT AND OVERSPED AIRSPEED LIMIT BY 5-10 KTS.

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FILED ON WX AVOIDANCE RTE FOR WX. WORKING WITH DISPATCH THROUGHOUT FLT TO ENSURE RTE WAS BEST FOR WX AVOIDANCE AND WAS TOLD IT WAS 'PERFECT' AND THAT WE WERE AT BEST ALT (FL350) ACCORDING TO PREVIOUS ACFT. DISPATCH SAID 'INT-CONT LIGHT CHOP AT 350' WOULD START IN APPROX 50 MI; SO I TURNED THE SEATBELT SIGN ON AND ALSO MADE A CALL TO THE FLT ATTENDANTS TO GIVE THEM A HEADS-UP. THEY INDICATED SVC WAS COMPLETE AND THEY WERE DOWN. DISPATCH SAID OUR FLT AHEAD ON SAME RTE HAD REMAINED AT FL350 AND HAD NOT DEVIATED -- WX RADAR SHOWED WHAT APPEARED TO BE ACTIVITY TO THE S BUT NOTHING ALONG OUR RTE. APPROX 5 MINS LATER; IN NOTHING WORSE THAN INTERMITTENT LIGHT CHOP; THE ACFT ABRUPTLY PITCHED UP WITH MORE THAN A MODERATE JOLT AND SIMULTANEOUSLY SPED UP. I IMMEDIATELY DISCONNECTED AUTOPLT AND AUTOTHROTTLES AND RETARDED THRUST TO IDLE. WE CLBED AT APPROX 2000 FPM WITH THRUST AT IDLE AND STILL OVERSPED THE AIRFRAME BY 5-10 KTS FOR APPROX 3 SECONDS. ALTDEV APCHED +1500 FT BEFORE I COLD CTL ACFT AND BEGIN A DSCNT IN NOW MODERATE TURB; DURING WHICH TIME I INSTRUCTED FO TO CHIME THE BACK AND THEN CALL TO MAKE SURE EVERYONE WAS OK. AT THAT TIME; ATC SAID 'SAY ALT' AND I INFORMED THEM THAT WE WERE NOW DSNDING BACK THROUGH FL360 AND HAD ENCOUNTERED SEVERE TURB. THEY ASKED WHAT ALT WE WANTED TO LEVEL OFF; AND I SAID FL330; WHERE IT WAS CONTINUOUS LIGHT CHOP AGAIN. FO VERIFIED EVERYONE HAD BEEN SEATED WITH NO INJURIES AND WE NOTICED NO APPARENT ACFT DAMAGE OR SYS FAILURES. BELIEVING BEFORE THE EVENT WE HAD NO TFC IN AREA; I ASKED ATC IF HE NEEDED TO FILE ANYTHING RELATIVE TO THE ALTDEV IN RVSM AND HE RESPONDED 'NO; THERE WAS NO OTHER TFC AROUND AND NO SEPARATION LOSS' AND THEN HE APOLOGIZED FOR NOT KNOWING THE RIDE WAS THAT BAD AND THAT OTHER ACFT HAD BEEN THROUGH THAT AREA NOT THAT LONG BEFORE. MY TAKE-AWAY FROM THIS INCIDENT WAS EXTREME GRATITUDE FOR HAVING TURNED ON THE SEATBELT SIGN IN ANTICIPATION OF THE TURB (EVEN THOUGH WE NEVER EXPECTED THE SEVERITY OF WHAT WE ENCOUNTERED); AND HOW FORTUNATE WE WERE THAT EVERYONE WAS ADHERING TO THE SIGN AND THAT WE HADN'T INJURED ANYONE. IT DEFINITELY COULD HAVE BEEN A FAR DIFFERENT OUTCOME AND IN THE FUTURE; I WILL MOST LIKELY EVEN BE MORE PROACTIVE WITH THE SIGN.