A B737-300 AFTER A NORMAL LNDG THE ACFT EXITED THE RWY APPROX 20 FT DUE TO POOR RWY BRAKING ACTION.

Narrative

AFTER A NORMAL LNDG AT JAC; ACFT SLID OFF THE END OF RWY 18 BY APPROX 20 FT. PROB AROSE BECAUSE OF POOR BRAKING ACTION NEAR THE END OF RWY AND INSUFFICIENT DISTANCE REMAINING TO STOP. PRIOR TO LNDG; BRAKING ACTION WAS RPTED AS FAIR (MU METERED AT ABOUT 40). THE ACFT WAS HVY (NEAR MAX LNDG WT); HIGH GUSTY WINDS (18 KTS GUSTING TO 27 KTS); AND POOR VISUAL REFS (SNOWY ENVIRONMENT/RWY) MADE IT DIFFICULT TO LAND (TOUCHDOWN) SOONER THAN 1000 FT FROM APCH END. WE RECEIVED A NEW BRAKING ACTION ADVISORY ONLY 1 MIN OR LESS PRIOR TO LNDG AND THAT WAS ON PRINTER. BRAKING ACTION WAS FAIR TO POOR. DECELERATION IN REVERSE THRUST PHASE SEEMED NORMAL; BUT AS REVERSE WAS STOWED AND AUTOBRAKES WERE OVERRIDDEN; THE DECELERATION RATE LESSENED CONSIDERABLY. BRAKES WERE INTO ANTI-SKID OP AND WE BEGAN SLIDING AS WE APCHED THE END. IT BECAME OBVIOUS THAT WE WOULD COME CLOSE OR DEPART THE RWY WITHOUT BETTER BRAKING ACTION. I CHOSE TO TRY A LAST MIN TURN SLIGHTLY OFF CTRLINE TO MISS RWY END LIGHTS. NO DAMAGE TO ACFT; RWY OR EQUIP; NO INJURIES.