ACR LGT EXPERIENCES A LOSS OF ACFT CTL AND ALT EXCURSION WHEN FLYING BTWN 2 CELLS IN A LINE OF TSTMS. RPTR CITES MODERATE TO SEVERE TURB; NO INJURIES. AN INSPECTION OF THE ACFT WOULD HAVE BEEN REQUIRED UPON LNDG AT MEM.

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LINE OF TSTMS SHOWING ON THE RADAR WHILE CRUISING AT FL370. ACCORDING TO THE RADAR WE HAD ABOUT 50 MI OF SPACE BTWN 2 CELLS IN WHICH TO FLY THROUGH. THIS WAS CONFIRMED BY VISUALLY LOCATING THE TOPS -- 1 TO THE S; AND 1 TO THE N; AS WE FLEW EBOUND. NO TSTMS COULD BE SEEN OR WERE PAINTING ON THE RADAR AT ANY ALT IN OUR PATH. HOWEVER; AS WE PASSED BTWN THE 2 CELLS WE ENCOUNTERED IMC CONDITIONS IN THE CIRRUS CLOUDS THAT WERE ORIGINALLY BELOW US. AFTER ABOUT 5 MINS IN THE CIRRUS WE ENCOUNTERED MODERATE AND POSSIBLE SEVERE TURB FOR ABOUT A MIN. PRIOR TO THIS; WE HAD ONLY BEEN ENCOUNTERING CONTINUOUS LIGHT AND OCCASIONAL MODERATE TURB. THE ACFT HIT AN UPDRAFT AT ONE POINT AND OUR ALT INCREASED 800 FT. WE IMMEDIATELY CORRECTED BACK TO OUR ASSIGNED ALT OF FL370. WE NOTIFIED ATC OF THE WX PROBS AND THEY SAID THE BEST RTE WAS DIRECT FT SMITH FOR TSTM AVOIDANCE. WE ACCEPTED THE CLRNC AND THE TURB SUBSIDED TO CONTINUOUS LIGHT. NO OTHER HVY TURB WAS ENCOUNTERED. NO CONFLICT WITH OTHER ACFT OCCURRED AND THE FLT LANDED IN MEMPHIS WITHOUT INCIDENT OR ANY CREW OR PAX INJURIES.