B757 ENCOUNTERED SEVERE TURB WHILE CLIMBING IN THE VICINITY OF TSTMS OVER MOUNTAINOUS TERRAIN.

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WE DEPARTED DENVER WBOUND; FO'S LEG. TYPICAL LIGHT CHOP ON CLBOUT TOWARD THE FRONT RANGE. BROKEN LAYER OF CLOUDS FROM 7000-9000 FT. OVER THE FRONT RANGE; VARIOUS BUILDUPS WERE OBSERVED. WE WERE GIVEN RADAR VECTORS TO AVOID A MAJOR BUILDUP S OF US. AT APPROX FL275; CLBING TO FL380; WE EXPERIENCED INTERMITTENT MODERATE CHOP. ATC ADVISED US THAT MODERATE CHOP WAS REPORTED FROM FL285-FL330. WE WERE IN AND OUT OF CLOUDS; AND THERE WERE NO SIGNIFICANT RETURNS ON RADAR IN FRONT OF US. AT FL280-FL330 WE EXPERIENCED SEVERE TURB. WE WERE UNABLE TO MAINTAIN WINGS LEVEL AND EXPERIENCED SHORT VERT UP AND DOWN DEVS OF 1000 FT OR MORE FROM OUR NORMAL VERT CLB. WE CLRED THE TOPS AT FL320. DURING THE VERT SPD EXCURSIONS; WE EXPERIENCED SIGNIFICANT PRESSURE AGAINST OUR SEATBELTS. FO WAS ABLE TO MAINTAIN AIRSPD OF AROUND 280 KTS THE ENTIRE TIME. THE FLT ATTENDANTS WERE TOLD TO REMAIN IN THEIR SEATS DURING THE PRE-DEP BRIEFING UNTIL WE CALLED. NO INJURIES WERE REPORTED BY FLT ATTENDANTS OR PAX. WE NOTIFIED ATC; DISPATCH; AND MAINT.