C401 PLT ENCOUNTERED MODERATE TO SEVERE ICING IN THE ROCKY MOUNTAIN FRONT RANGE AREA IN ZDV CLASS E AIRSPACE.

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IMMEDIATELY PRIOR TO MY DEP AT JEFFCO COUNTY ARPT; A PLT AHEAD OF ME RPTED THE TOPS OF THE CLOUDS WERE 10300 FT. HE ALSO RPTED NO TROUBLE IN THE CLBOUT AND NO ICE. I EVEN REMEMBER HIM SAYING HE WAS WITNESSING A BEAUTIFUL SUNSET. BASED ON THIS OBSERVATION; I DECIDED TO TAKE OFF. DURING MY PREFLT; I VERIFIED ALL DEICING SYS WERE WORKING PROPERLY; ALSO I DID A WT AND BAL AND DETERMINED THE ACFT TO BE WITHIN LIMITS. AFTER TKOF WE BEGAN TO CLB OUT AS NORMAL WITHOUT ANY PROB. AT FIRST; WHEN IN IMC WE ACCUMULATED NO ICE WHATSOEVER WHICH SEEMED TO CONFIRM THE PLT RPT. DURING THE FIRST 2000 FT OR 3000 FT OF THE CLB WE STILL HAD NO ICE. ONCE WE REACHED AN ALT OF APPROX 9000 FT; WE STARTED TO ACCUMULATE ICE AT AN ALARMING RATE. I RPTED THIS TO ATC. THEY ASKED ME IF I WANTED A DIFFERENT ALT AND I ELECTED TO CLB; AS I KNEW IT WAS CLR ABOVE. SOON AFTER MY VERT SPD WENT FROM A STEADY 500 FPM CLB TO ABOUT 200 FPM OR 100 FPM. I WAS NOT UTILIZING MAX PWR AT THIS TIME. I PROCEEDED TO APPLY MAX PWR AND BEGAN TO CLB AGAIN. WE GAINED ANOTHER 500 FT OR SO AND THE ICE WAS STILL ACCUMULATING AT A SURPRISING RATE. I LIKE TO KEEP MY OPERATING TEMPS BELOW A CERTAIN LEVEL AND THEY STARTED TO EXCEED MY PERSONAL LIMITS; SO I ELECTED TO LAND AT A NEARBY ARPT. ATC GAVE ME A VECTOR TO GREELEY ARPT AND I LANDED WITHOUT INCIDENT. I BELIEVE THAT I ENCOUNTERED A PATCH OF FREEZING RAIN; WHICH ACCOUNTED FOR THE RAPID BUILDUP OF ICE. HINDSIGHT IS ALWAYS 20/20; BUT I BELIEVE THE ACFT AHEAD OF ME PROBABLY MISSED AREAS OF FREEZING RAIN AND TEMPS. I BELIEVE HE PROBABLY CLBED FASTER THAN I DID AS WELL. JUST BECAUSE ONE PLANE DOES NOT GATHER ICE DOESN'T MEAN ANOTHER ACFT WON'T; ESPECIALLY IN AN ENVIRONMENT AS UNPREDICTABLE AS THE FOOTHILLS OF THE COLORADO MOUNTAINS. NOW THAT IT IS CLOSE TO WINTER THERE WILL BE AIRMETS FOR ICING EVERY DAY. I DON'T BELIEVE THIS SYS IS RELIABLE ENOUGH TO WARN PLTS OF POSSIBLE DANGER AREAS. I FEEL THERE SHOULD BE A BETTER SCALE FOR PLTS TO USE WHEN DETERMINING WHETHER OR NOT TO TAKE OFF.