A C180H CFI RUNS INTO LOWERING VISIBILITY AND ENACTS AN IMC IN VFR FLT INCIDENT 55 MI NW OF GRR; MI.

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I WAS FLYING VFR AT THE CRUISING ALT OF 4500 FT MSL HDG 280 DEGS WHEN I APCHED WX IN MY PATH. AS I WAS WELL ESTABLISHED BTWN CLOUD LAYERS; AND RECEIVING RADAR ADVISORIES FROM GRAND RAPIDS; I CHOSE TO CONTINUE FLT OVER THE BROKEN CLOUD LAYER AND CONTINUE WHAT APPEARED TO BE ADEQUATE CLOUD CLRNCS. I WAS NOTIFIED BY ATC OF PRECIP ALONG MY COURSE; BUT DUE TO FLT CONDITIONS AT THE TIME CHOSE TO MAINTAIN MY HDG AND ALT. SHORTLY AFTER ENTERING THE AREA OF PRECIP; I DETERMINED THE FLT VISIBILITY AND CLOUD CLRNCS TO BE BELOW THAT OF CLASS E REQUIREMENTS. I IMMEDIATELY TURNED TO A HDG (330 DEGS) THAT PROVIDED A CLR VIEW OF THE CLOUDS SURROUNDING ME; AND DSNDED TO 2500 FT MSL SO AS TO REMAIN BENEATH ANY OTHER CLOUD LAYERS. I FEEL THAT AS A CFI AND CURRENT INST PLT; I BECAME OVERLY COMFORTABLE FLYING IN AN ENVIRONMENT OF LIMITED VISIBILITY; ESPECIALLY WHILE RECEIVING RADAR ADVISORIES. COMPOUNDING THAT; I SHOULD HAVE REALIZED THAT THE PRECIP WOULD BEGIN TO 'CLOSE THE GAP' THAT I WAS FLYING IN. IN THE FUTURE; I NEED TO USE MY AVIATION KNOWLEDGE AND EXPERIENCE TO REMAIN CLR OF POTENTIAL VISUAL OBSTRUCTIONS; OR FILE IFR FOR THOSE FLTS THAT MAY SEEM MARGINAL. THIS WAS SURELY A GOOD LESSON LEARNED; AND ONE THAT I WILL PASS ON TO ALL MY STUDENTS.