UNAUTH PENETRATION OF AIRSPACE; PROX OF CTL ZONE. IMC IN VFR FLT.

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WAS RETURNING VFR FROM PEORIA; IL; TO ROCKFORD; IL. CONTACTED KANKAKEE FSS TO GET AN RFD WX UPDATE. I WAS TOLD RFD WX WAS 4000 FT OVCST AND 7 MI VISIBILITY AND THAT THE RFD TERMINAL FORECAST HAD NOT BEEN AMENDED. THE RFD FORECAST WAS 30 SCATTERED CEILINGS 50 BROKEN 2500 OVCST OCCASIONAL 30 BROKEN TILL XA00 AM. AT XA40 AM I INITIATED THE ILS RWY 7 APCH AT RFD ARPT. THE ROCKFORD TWR CLOSES FROM 11 PM - 6 AM. I WAS IN VFR CONDITIONS AND COULD SEE STARS ABOVE AND THE GND BELOW. THIS IS A RELATIVELY NEW APCH AT ROCKFORD AND THIS WAS JUST A PRACTICE APCH IN VFR CONDITIONS TO FAMILIARIZE MYSELF WITH THE APCH. I DIDN'T CONTACT ZAU APCH BECAUSE THE WX RPT FROM FSS AND MY OWN OBSERVATIONS LED ME TO BELIEVE THAT THE RFD ARPT WAS IN VFR CONDITIONS AND THAT THE CTL ZONE WOULD NOT BE ACTIVE. I ADVISED ON CTAF 118.3 ON MY INTENTIONS. I KEYED ON THE APCH LIGHT SYS AND COULD SEE THE LIGHTS ALL THE WAY FROM THE OM. I SHOT THE APCH DOWN TO DECISION HT AND LEVELED THE ACFT AND STARTED A CLB BACK UP TO 1000 FT AGL. AT ABOUT 300-400 FT I FOUND ALL OUTSIDE REFS OBSCURED. I CONTINUED TO CLB AND CONTACTED ZAU APCH FOR AN IFR CLRNC. I REQUESTED AND RECEIVED AN IFR CLRNC BACK INTO RFD. THE WX RAPIDLY DETERIORATED AFTER THIS. LATER; LOOKING AT A WX PRINTOUT; I REALIZED THAT I WAS IN THE CTL ZONE WITHOUT A CLRNC FOR APPROX 3-5 MINS. THE ORIGINAL WX FORECAST WAS VERY INACCURATE AND SUBSEQUENT FORECASTS WERE AMENDED TO REFLECT THE MUCH LOWER WX. AT XA31 AM; HAD I BEEN GIVEN THE RFD WX RPT; I WOULD HAVE CONTACTED CTR BUT DUE TO THE DELAY BTWN WHEN THE OBSERVATION IS TAKEN AND THE TIME IT TAKES TO GET INTO THE SYS AND BE RELAYED CONTRIBUTED TO MY BEING IN A JUST ACTIVATED CTL ZONE WITHOUT A CLRNC.