MD80 FLT CREW ON ARR INTO SAT EXPERIENCE A BRIEF ENCOUNTER WITH SEVERE TURB AT FL240.

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FLYING THE MARCS 7 ARR TO SAT ON A CLRNC TO FLY DIRECT CWK WE ENCOUNTERED A BRIEF PERIOD OF SEVERE TURB. AT FL240 AND 300 KIAS; WE WERE FLYING ABOVE A CLOUD LAYER AND WERE MAINTAINING AN ACTIVE RADAR WATCH IN THE WX/TURB MODE. IN THE DARK; I SAW A COUPLE OF CLOUD TOPS ABOVE THE LAYER AT ABOUT OUR ALT. WE WERE NOT FAR ABOVE THE LAYER; THE RIDE WAS SMOOTH; AND THE RADAR DID NOT PAINT ANY PRECIP OR TURB IN OUR VICINITY. THE CLOSEST PRECIP SHOWN WAS ABOUT 40 NM AHEAD OF US. I THOUGHT THE TOPS WERE JUST RAGGED TOPS OF THE LAYER WE WERE OVER. SINCE THEY WERE AT OUR ALT I TURNED ON THE SEATBELT SIGN AS A PRECAUTION. ABOUT 30 SECONDS TO A MIN LATER WE HIT TUE TURB. IT WAS BRIEF BUT VIOLENT. IT FELT AS THOUGH THE ACFT WAS STRONGLY PUSHED FROM DIRECTLY BELOW; THE FLT INSTS WERE NOT READABLE; AND THE AUTOPLT DISCONNECTED UNCOMMANDED. THE EVENT LASTED FOR POSSIBLY 5-15 SECONDS. THE ACFT SETTLED OUT ABOUT 100 FT LOW; L WING DOWN ABOUT 15-20 DEGS; NOSE DOWN 2-3 DEGS; AUTOPLT OFF. I RECOVERED THE ACFT. THEN THE FO RPTED THE TURB TO ZHU. I HAD HIM GET US A CLB CLRNC AND WE CLBED TO FL260. AS WE WERE CLBING I HAD THE FO CALL THE FLT ATTENDANTS AND INQUIRE ABOUT ANY POSSIBLE INJURIES. THERE WERE NONE. ONCE LEVEL; I SPOKE WITH THE FLT ATTENDANTS AND WAS AGAIN TOLD THERE WERE NO INJURIES. THEY FURTHER RPTED THE CART WAS IN THE AISLE AT THE TIME AND WAS LIFTED OFF THE DECK BY THE TURB AND THAT SOME TOMATO JUICE ON THE CART WAS THROWN ONTO THE OVERHEAD. ON ARR AT SAT I ENTERED THE SEVERE TURB INTO THE MAINT LOG GIVING OUR ALT; AIRSPD; ZERO FUEL WT; FUEL ABOARD; ESTIMATED GROSS WT; AND ESTIMATED DURATION OF THE EVENT. I RPTED THE EVENT AND THE LOCATION OF THE TURB TO DISPATCH; AND ALSO INFORMED MAINT OF THE SEVERE TURB MAINT ENTRY.