PA34 PILOT ENCOUNTERS SEVERE TO EXTREME TURBULENCE AND SEVERE ICING WHILE TRANSITING A LARGE CLOUD ON AN IFR FLIGHT.

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I WAS FLYING IN VMC CONDITIONS; BUT WITH CLOUDS AND IMC CONDITIONS IN THE AREA; AT 13000 FT MSL ON AN IFR FLT PLAN. I WAS ISSUED A DSCNT FROM 13000 FT TO 12000 FT AND WAS BEGINNING THAT DSCNT. SHORTLY INTO THE DSCNT; I NOTICED THAT MY AIRSPD WAS INCREASING DRAMATICALLY; AND INSTEAD OF DSNDING I WAS CLBING. NORMAL DSCNT SPDS AT THIS ALT ARE ABOUT 160-165 KIAS (JUST AT THE BOTTOM OF THE YELLOW); WITH A DSCNT RATE OF 500 FPM. THE AIRPLANE WAS FLYING ON AUTOPLT AT THE TIME. BUT IN THIS CASE I NOTICED THAT THE AIRSPD HAD SIGNIFICANTLY EXCEEDED THIS AND WAS CLBING TOWARDS 200 KIAS (RED LINE ON THIS AIRPLANE IS 204 KIAS) AND WAS STILL NOT DSNDING; AND IN FACT I HAD CLBED TO AT LEAST 13500 FT BY THEN; AND WAS ABOUT TO ENTER A CLOUD. THIS SET OFF ALL MY PERSONAL ALARM BELLS AS I EXPECTED THAT SHORTLY AFTER PENETRATING THE CLOUD I WOULD HIT TURB; AND WITH THIS UPDRAFT I EXPECTED VIOLENT TURB; AND I WAS WELL ABOVE THE STRUCTURAL MANEUVER SPD. I IMMEDIATELY DISENGAGED THE AUTOPLT; REDUCE PWR TO IDLE; AND SLOWLY PULLED THE NOSE UP TO BLEED OFF AIRSPD. THEN I PENETRATED THE CLOUD; AND ALMOST IMMEDIATELY HIT THE TURB; AND THANKFULLY BY THEN THE AIRSPD WAS DOWN TO AROUND 150 KTS; STILL ABOVE THE MANEUVER SPD; (MANEUVER SPD AT OUR WT WAS ABOUT 135 KIAS) BUT NOT NEAR THE RED LINE AS IT WAS BEFORE. THE TURB WAS MORE AN IMPACT THAN TURB; AND EVERYTHING IN THE AIRPLANE WAS FLYING AROUND THE CABIN. THIS WAS THE WORST TURB I HAD EVER EXPERIENCED IN OVER 33 YRS OF FLYING. (I WOULD CLASSIFY IT AS EXTREME; I DO NOT THINK THAT THE TERM SEVERE IS ADEQUATE TO DESCRIBE WHAT WE WERE IN.) BY NOW WITH ENGS AT IDLE; AND SPD AT ABOUT 140 KIAS; WE WERE CLBING WITH THE VSI PEGGED AT 2000 FPM; AND WERE CLBING THROUGH 14500 FT; THEN WE HIT THE DOWNDRAFT; AND AGAIN IT WAS MORE OF AN IMPACT THAN TURB. I ADDED FULL PWR; AND ESTABLISHED 110 KIAS (THE NORMAL CLB SPD) AND BY THIS TIME WE WERE DSNDING WITH THE VSI PEGGED IN A DSCNT OVER 2000 FPM; AND SOON WE WERE DSNDING THROUGH 10000 FT. THIS UPDRAFT/DOWNDRAFT CYCLE WENT ON FOR ABOUT 2-3 ITERATIONS. THE NEXT ISSUE WAS ICE. I DIDN'T HAVE MUCH TIME TO LOOK AT THE WINGS; BUT THERE WAS BY NOW NEARLY 3/4 INCH OF MIXED ICE ON THE WING LEADING EDGES. (WE HAD ONLY BEEN IN THIS CLOUD FOR 2-5 MINS AT THE MOST.) THEN WE EXITED THE CLOUD; AND NOW WE WERE IN WHAT I WOULD DESCRIBE AS SEVERE TURB FOR THE NEXT 10 MINS. DURING ALL THIS TIME I TRIED TO CONTACT EITHER ZSE; OR GREAT FALLS APCH (I CANNOT REMEMBER WHICH; AS IT WAS AT THIS TIME THAT I WAS SWITCHED) ON THE RADIO TO ADVISE THEM OF MY ALTDEVS; I WAS NOT ABLE TO GET A REPLY; UNTIL I LEFT THE CLOUD; AND WAS NOW IN THE CALMER SEVERE TURB. I ADVISED THEM OF THE ALTDEVS; THE EXTREME TURB; AND THE SEVERE ICING ENCOUNTER; AND MADE SURE THAT THEY WERE AWARE NOT TO SEND ANYONE NEAR THAT AREA.