MD80 FLC HAS EXCURSION FROM ASSIGNED ALT WHEN ENCOUNTERING A LIFTING AIR MASS.

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FLT PATH WAS XING A COLD FRONT ENRTE TO IND. TYPICAL SPRING WX WITH RAPIDLY CHANGING WX PATTERNS. AT FL310 RADAR WAS PAINTING PRECIP ON 160 MI SCALE. RETUNED WHEN PRECIP BEGAN PAINTING ON 80 NM SCALE. RETURNS WERE DISAPPEARING AS WE APCHED; EVEN WITH CONTINUAL ANTENNA ADJUSTMENTS INDICATING THE HVY PRECIP WAS BELOW OUR CRUISE ALT. AS WE APCHED TO WITHIN 20 MI OF WX; WE COULD SEE RAGGED TOPS INDICATING POTENTIAL TURB. FO WAS FLYING ACFT SO I DIRECTED HIM TO TURN TO AVOID THE RAGGED TOPS. ASKED FOR AND RECEIVED CLRNC FROM CTR TO DEV. FO USED SHALLOW BANK (10 DEGS) TO INITIATE TURN AND BY THE TIME I DIRECTED MORE BANK TO TURN BEFORE THE TOPS; WE ENTERED CLOUDS AND EXPERIENCED MODERATE TURB AND STRONG UPDRAFT. AUTOPLT DISENGAGED AND FO BEGAN FORWARD PUSH ON CTLS. AS ALT CLBED; I ASSISTED ON CTLS TO PUSH OVER. WE HAD CLBED 800 FT BEFORE CLB ARRESTED AND DSCNT BEGAN. NO CONFLICTS WITH ANY ACFT. NO OTHER ACFT SHOWN ON 20 MI RANGE OF TCASII. NO CONFLICTS OR DEV MENTIONED OR NOTED BY CTR. FO HAD ONLY APPROX 110 HRS IN ACFT AND WAS HESITANT TO USE MORE FORCE TO CTL PITCH DUE TO HIS LIMITED TIME ON ACFT AND HIS HVY EXPERIENCE ON BOEING ACFT WHERE CTL RESPONSE IS MORE ACTIVE. INCIDENT COULD HAVE BEEN PREVENTED BY EARLIER RECOGNITION OF POTENTIAL WX CONFLICT AND DEVIATING SOONER. TURB WAS RPTED TO CTR WITH LOCATION NOTED.