MD80 CREW WAS DISPATCHED WITH AN MEL THAT RESTR THE ACFT TO A DRY RWY. WHEN THE DEST WAS GETTING LIGHT RAIN; THE CREW DIVERTED TO THE NEAREST SUITABLE ARPT WITH A DRY RWY.

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FLT FROM PVD-ORD DIVERTED INTO PIT DUE TO THE LIMITATIONS IMPOSED BY MEL 30-01; WHICH STATES THAT FLT WITH A MISSING MAIN GEAR SPLASH DEFLECTOR IS OKAY; AS LONG AS THE RWY CONDITIONS ARE DRY. WHEN FLT DEPARTED FROM PVD ON DEC/TUE/03; THE DEP RWY WAS CLR AND DRY; AND THE FIELD RPT IN THE FLT PAPERWORK SHOWED THAT THE RWYS AT ORD WERE ALSO DRY. WHILE ENRTE; ATIS RPTS INDICATED THAT LIGHT RAIN WAS BEGINNING TO FALL AT ORD. DISPATCH CONTACTED US AT ABOUT THIS SAME TIME TO ADVISE US THAT THEY WERE AWARE OF THE CDL LIMITATIONS AND WERE LOOKING FOR AN ALTERNATE LNDG SITE FOR US. IT WAS DETERMINED THAT PIT WAS THE CLOSEST SUITABLE ALTERNATE WITH DRY CONDITIONS; SO WE DIVERTED INTO PIT; SWAPPED AIRPLANES WITH A FLT ARRIVING FROM DFW; AND CONTINUED ON TO ORD. ALTHOUGH I DON'T BELIEVE THAT VIOLATIONS OF ANY KIND OCCURRED ON THIS FLT; THE POTENTIAL CERTAINLY WAS THERE. THE REPAIR TO THE SPRAY DEFLECTOR HAD BEEN DEFERRED SINCE DEC/MON/03; AND WITH WINTER WX CONDITIONS THROUGHOUT THE COUNTRY; IT IS ENTIRELY POSSIBLE THAT WE (OR SOME OTHER CREW) COULD HAVE FOUND OURSELVES IN A SIT WHERE WE WOULD HAVE HAD NO CHOICE BUT TO LAND ON A WET OR CONTAMINATED RWY. THE LESSON LEARNED FROM THIS INCIDENT IS TO BE EVEN MORE AGGRESSIVE IN CORRELATING MEL/CDL LIMITATIONS WITH ACTUAL AND FORECAST WX CONDITIONS AND ANTICIPATING THEIR IMPACT ON SUBSEQUENT FLT OPS.