A C172 ENCOUNTERED FORECAST ICING CONDITIONS NEAR LOZ.

Narrative

DURING AN IFR XCOUNTRY FROM LUK TO MCN; WE ENCOUNTERED LIGHT ICING ABOUT 20 NM NNW FROM THE LOZ VOR. THE WINGS LOOKED JUST SLIGHTLY FROSTY; ALMOST AS THOUGH SOMEONE HAD BEEN BREATHING ON THE WINGS. THERE EVEN APPEARED TO BE A SLIGHT 'SHADOWING' OF THE WINGS. WE EXERCISED GOOD CRM AND IMMEDIATELY DECIDED TO DIVERT TO THE NEAREST ARPT; WHICH THANKFULLY HAD A VOR APCH. HOWEVER; WHILE WE DSNDED FROM THE MEA FOR THE INST APCH; WE PICKED UP MODERATE MIXED ICING. THE TEMP AT THE MEA (5000 FT) WAS 30 DEGS F. I ASSUMED THAT A DSCNT OF 3000 FT FOR THE APCH WOULD PREVENT ADDITIONAL ICE FROM FORMING. WAS I IN FOR AN UNPLEASANT SURPRISE! WE QUICKLY PICKED UP BTWN 1/2 - 3/4 OF AN INCH ON THE ENTIRE AIRPLANE; AND THE TEMP GAUGE NEVER MOVED FROM 30 DEGS F DURING THE ENTIRE APCH. I AM WRITING THIS FORM TO ADMIT SOME MISTAKES I MADE AND REVEAL SOME THINGS I LEARNED. I WAS WRONG TO THINK THAT I COULD FLY THROUGH AN AREA FORECASTED TO HAVE LIGHT TO MODERATE RIME ICING IN THE CLOUDS. I ASSUMED THAT BECAUSE LAYERS WERE RPTED THAT I WOULD EASILY FIND AN ALT THAT WOULD KEEP ME OUT OF THE CLOUDS. I PUT MYSELF IN A SIT WHERE I FELT I WOULD HAVE TO DECLARE AN EMER BEFORE IT WAS TOO LATE. I COULD HAVE NEVER IMAGINED HOW QUICKLY THE AIRPLANE WENT FROM 'FEELING LIKE' A C172 TO 'FEELING LIKE' A HVY B747. WE WERE A VERY HVY C172. WE TOOK OFF AT MAX GROSS WT; 3 PAX AND FULL FUEL IN A C172 WITH EXTENDED FUEL TANKS. WE HAD A GPS ON BOARD THAT REALLY ALLOWED ME TO SEE THE AFFECT THE ICE HAD ON OUR AIRPLANE. AS WE PICKED UP MORE AND MORE ICE; I NOTICED THAT THE GND SPD INDICATED ON THE GPS CONTINUED TO DECREASE. ANOTHER THING I LEARNED IS THAT IT'S REALLY EASY TO SPOT ICE ACCUMULATION ON THE BLACK TIRES. I WILL NEVER FLY IN KNOWN OR FORECASTED ICING CONDITIONS EVER AGAIN.