A BE35 PLT; FLYING VFR; PICKED UP THE ATIS AT BJC DESCRIBING VFR WX. WHEN HE CONTACTED THE TWR AT BJC; HE WAS TOLD THE ARPT HAD DETERIORATED TO IMC AND THAT HE HAD ENTERED THEIR AIRSPACE. THE PLT REVERSED COURSE AND REQUESTED AN IFR CLRNC FROM DEN TRACON. BY THE TIME THE RPTR RETURNED FOR LNDG; THE ARPT HAD IMPROVED TO VMC.

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VFR FLT FROM HUT TO BJC. VMC ENRTE WITH BJC FORECASTING MVFR (1100 BROKEN P6) WITH LIGHT TO MODERATE ICING ABOVE 7000 FT. I DID NOT WANT TO FLY IFR BECAUSE MINIMUM ENRTE ALTS IN THE DENVER AREA ARE ABOUT 7000 FT. MY WIFE IS A LICENSED VFR PLT AND WAS PERFORMING PNF DUTIES. WE ASKED FOR AND RECEIVED RADAR ADVISORIES FROM DEN APCH AND GOT CLRNC THROUGH THE CLASS B AIRSPACE AT 5500 FT DIRECT TO BJC. MY WIFE COPIES BJC ATIS INFO AT 20 MI OUT (020 DEGS AT 7 KTS 15 D2 1300 FT BROKEN 2000 FT OVCST; ALTIMETER 30.28; 6/-1 ILS RWY 29R MODERATE RIME 2/20 CLOUD) AND WE WERE STILL WITH DEN APCH AT 6 MI OUT WITH GOOD VFR. I ASKED DEN APCH IF THEY WANTED US TO GO TO BJC TWR AND RECEIVED NO ANSWER. NOT WANTING TO PENETRATE BJC AIRSPACE WITHOUT RADIO CONTACT; I CALLED THEM ON VHF #2 AND RPTED MY POS AND INTENTION TO LAND. THEY IMMEDIATELY ADVISED ME THAT BJC WAS IFR (300 OVCST 1/4 MILE I BELIEVE) AND THAT I WAS ENTERING THEIR AIRSPACE. I IMMEDIATELY REVERSED COURSE; CALLED DEN APCH AGAIN; GOT AN IFR CLRNC AND RETURNED TO LAND WITH VFR CONDITIONS AGAIN EXISTING AT BJC. WE HAD HEARD ANOTHER BONANZA RPTING NO ICE IN THE CLOUDS AT 8000 FT; SO I CHANGED MY MIND ABOUT CLBING ABOVE THE FREEZING LEVEL IN ORDER TO GET AN IFR CLRNC. IN RETROSPECT; I BELIEVE MY DECISIONS WERE CORRECT. BJC WAS RPTING VFR WHEN WE GOT THE ATIS AND A MOMENTARY SNOW SHOWER CAUSED IMC. I HAD FLT FOLLOWING AND AM VERY FAMILIAR WITH THE AREA AROUND BJC SO MVFR FOR 1-2 MINS WAS NOT A SURPRISE.