A C210 AT 16000 FT ENCOUNTERED UNEXPECTED ICING N OF CIM VORTAC AND DESCENDED TO 12000 FT. PLT LANDED BEFORE HIS DEST TO CHK FOR FURTHER ICING CONDITIONS.

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IFR CLRNC TO BJC FROM 94E AT 16000 FT MSL. I HAD BEEN ABOVE CLOUD DECK FROM ABQ TO CIM. AT CIM I REQUESTED AND RECEIVED FROM DENVER CTR FL160. THIS ALT PUT ME ABOVE RISING CLOUD DECK. AT 43 NM; 358 DEG RADIAL FROM CIM I ENTERED CLOUDS AT -20 DEG CELSIUS. AFTER ABOUT 3 MINS I FLEW THROUGH AN AREA OF MODERATE MIXED/RIME ICING AND REQUESTED AN IMMEDIATE DEV R OF COURSE. DENVER ATC COORD AND ASKED IF I WANTED HIGHER OR LOWER; REQUESTED LOWER AND WAS PERMITTED TO 12000 FT. AFTER 2 TO 3 MINS AND AT FL120. I ENTERED AREA OF BROKEN TO SCATTERED CLOUDS. I TOLD ATC I COULD RETURN TO V611. AT 12000 FT I CANCELED IFR AND PROCEEDED TO PUB TO CHK WX FROM PUB TO BJC. THIS WAS FLT INTO INADVERTENT ICING. I FLY NEAR THE E SIDE OF THE ROCKIES ALL YEAR AROUND AND HAVE STUDIED THE WX IN DEPTH. ICE THIS TIME OF YEAR IS ALWAYS A POTENTIAL. ALTHOUGH I HAD CHKED DUATS; HAD CHKED ABQ FLT WATCH; HAD GUARDED FLT WATCH ON COM #2; UPDATED WX CONDITIONS AT LVS; RTN; TAD; PUB; I GOT CAUGHT. NO PIREPS ON ICING AND ICING SIGMETS WERE N OF PUB. THINKING ABOUT WHAT I SHOULD HAVE DONE; I MIGHT HAVE CHOSEN VICTOR AIRWAY FROM CIM - FOGLE - PUB WHICH WOULD GONE E OF RATON PASS (LOWER GND). I BELIEVE MY ICING CONDITION WAS FROM AN 'UP SLOPE;' IE WINDS FROM E/SE CAUSING LIFT TO A WET CLOUD (OROGRAPHIC LIFT). ALTHOUGH I DID NOT DECLARE AN EMER TO ATC... I FELT AN IMMEDIATE DEV (R) TO LOWER GND WAS NECESSARY TO GET TO A NON-ICE LEVEL.