A B737-300 CREW ENCOUNTERED A 20 SECOND SEVERE TURB UPSET WITH FLT ATTENDANTS AND PAX SEATED.

Narrative

ABOUT 40 MI N OF RBS VOR ON CLBOUT; ENCOUNTERED A SEVERE TURB EVENT CLBING THROUGH 20.5K ENRTE TO 23K. FLT ATTENDANTS HAD BEEN ASKED TO 'STAY DOWN' AND WERE AT THE TIME SEATED. SEATBELT SIGN WAS ON AND ALL PAX WERE SEATED. NO INJURIES OCCURRED. ABOUT 20 SECONDS IN DURATION; WITH MINIMAL G-LOADING; MAYBE +1.5 - 1.0. WX RADAR WAS ON AND PAINTING A LARGE AREA OF 'GREEN' WITH SOME YELLOW/RED TO FAR SIDES OF SCOPE (CLR ON EITHER SIDE OF SMALL GREEN AREA IN FRONT OF US). AS WE APCHED THE GREEN CELLS IN FRONT OF US; A BREAK OCCURRED IN THE CLOUDS AND WE SAW A FAIRLY LARGE CELL IN FRONT OF US AND AN OPENING TO THE L (SE). WE INFORMED ATC OF OUR DEV AS WE WERE TURNING. THE EVENT OCCURRED AFTER ABOUT 20 DEGS OF TURN AWAY FROM THE LARGER CELL ON OUR NOSE (WE WERE ON THE WESTERN EDGE OF THE SMALLER CELL; AS WE WERE GOING BTWN THE 2 'GREEN' CELLS). CTL WHEEL WAS ALMOST FULL R TRYING TO STOP THE LEFTWARD ROLLING MOMENT. REQUIRED SIGNIFICANT FORWARD CTL TO RIGHT THE ACFT. RPT FILED WITH DISPATCH AND MAINT IMMEDIATELY. REQUEST SENT TO GET ACFT MECH TO INSPECT ACFT.