A VFR C172 FLEW INTO CLOUDS WHILE TRANSITING GYY CLASS D AIRSPACE.

Narrative

I WAS FLYING OUR CLUB C172SP FROM OSHKOSH TO A PLANNED FUEL STOP AT VERMILLION COUNTY ARPT (DNV). WHILE TRANSITING THE CHICAGO LAKEFRONT VFR FLYWAY FROM THE N TO THE S; I VIOLATED PROPER CLOUD SEPARATION REQUIREMENTS FOR VFR FLT. THIS OCCURRED AS I WAS OVERFLYING THE GYY CLASS D AIRSPACE. I WAS RECEIVING FLT FOLLOWING FROM CHICAGO APCH. AS I WAS EXITING THE FLYWAY; THE CEILINGS BEGAN TO DROP. CHICAGO APCH MANAGED OUR TRANSITION OVER THE GYY CLASS D AIRSPACE AND ADVISED WE MAINTAIN 2100 FT MSL. AS WE BEGAN TO SKIM THE BASES OF THE OVCST CLOUD DECK; I CHKED THE GYY ATIS AND FOUND THE CEILING RPTED AS 1800 FT OVCST WHICH WAS 2350 FT MSL. I WAS BRIEFLY FLYING IN AND OUT OF THE THIN CLOUD BASE OCCASIONALLY IN IMC. I TURNED S WHILE OVER GYY ON MY PLANNED RTE EXPECTING TO FIND HIGHER CEILINGS AND FOLLOWING CHICAGO APCH INSTRUCTIONS TO MAINTAIN NO LOWER THAN 2100 FT MSL WHILE TRANSITING THE CLASS D AIRSPACE. ONCE OUT OF THE CLASS D AIRSPACE; I IMMEDIATELY DSNDED TO AN ALT WELL CLR OF THE CLOUDS AND PROCEEDING TO LAND AT GRIFFITH-MERRILLVILLE ARPT (05C) 6 MI S OF GYY AND JUST 2 MI OUTSIDE THE CLASS D AIRSPACE. I TOOK THIS ACTION TO AVOID ANY POSSIBLE FURTHER INADVERTENT FLT INTO IMC. EVEN THOUGH I RECOGNIZED MY PROX TO THE CLOUDS AS WE APCHED THE GARY CLASS D AIRSPACE; I CHOSE TO FOLLOW THE ATC ALT RECOMMENDATION RATHER THAN DSND TO MAINTAIN PROPER CLOUD CLRNC. I SHOULD HAVE INDICATED TO ATC THAT I WAS UNABLE TO MAINTAIN VFR AT THE ASSIGNED ALT AND REQUESTED LOWER. ADDITIONALLY; I DID NOT MONITOR GARY ATIS SOON ENOUGH TO RECOGNIZE THE CEILING LIMITATION. I COULD HAVE DIVERTED S SOONER AND AVOIDED THE CLASS D AIRSPACE JUST TO THE W WHERE I COULD HAVE MAINTAINED PROPER VFR CLOUD CLRNCS AND LANDED AT LANSING ARPT (IGQ). I FOUND LATER THAT CEILING CONDITION THERE WERE SLIGHTLY BETTER. I BELIEVE I COULD HAVE ACTED MORE QUICKLY TO INFORM ATC OF THE SITUATION AS IT WAS RECOGNIZED AND REQUESTED LNDG AT GARY (GYY) WHICH MAY HAVE BEEN THE MOST PRUDENT ACTION. THE GARY ARPT WAS CLRLY IN SIGHT AS WE CROSSED OVER IT. WE LATER RESUMED OUR FLT UNDER AN IFR FLT PLAN WITH A DIFFERENT PIC.