ALTDEV ALT EXCURSIONS ACCOUNT OF TSTM ACTIVITY.

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THE FLT WAS PLANNED FROM RAP DIRECT TO FSD. IT WAS VMC FOR THE FIRST HALF OF THE TRIP TO THE MISSOURI RIVER. A WIDE AREA OF TSTMS EXTENDING FROM NORTHERN NEBRASKA UP TO ABR IN SD AND ON TO FARGO; ND; WAS EXPECTED DUE TO A SLOW MOVING COLD FRONT FROM ONL TO MHE TO HON TO ABR. THERE WERE 4 CONVECTIVE SIGMETS COVERING VARIOUS SECTIONS BOTH N AND S OF THE RTE. MY PLAN WAS TO USE MY STORMSCOPE TO AVOID BOTH AREAS OF STORMS BEFORE THEY GREW TOGETHER; OR FLY S OF THE SYS OF STORMS; OR RETURN TO PIR OR RAP WHICH WERE TO REMAIN VFR. BY THE TIME I GOT TO THE MISSOURI; THE STORMS HAD FORMED A SOLID LINE BUT STILL REMAINED OPEN JUST S AND E OF ONL; NE. I WAS FLYING AT 7000 FT MSL ALONG THE MISSOURI WITH GOOD GND CONTACT; OCCASIONAL LIGHT SHOWERS; AND LIGHT TO MODERATE TURB. ABOUT 15 MI W OF YNK ON THE 270 DEG RADIAL; THE STORMSCOPE SHOWED 2 CLUSTERS WITH ABOUT A 15 MI GAP IN BTWN. I FELT THE GAP WAS LARGE ENOUGH TO PRESUME NOTHING WORSE THAN MODERATE TURB. THE WX IN FSD WAS STILL VFR WITH LIGHT WINDS AND CLOSE ENOUGH TO SUGGEST THAT THIS WAS THE BEST PLACE TO CROSS THE FRONT. I REQUESTED A DSCNT TO 5000 TO STAY BELOW THE BASES AND WAS TOLD TO RPT LEAVING 6000. IT QUICKLYY BECAME APPARENT THAT I WOULD HAVE TO ENTER IMC TO CROSS THE FRONT. I RPTED LEAVING 6000. AFTER ENTERING THE CLOUDS; I WAS HIT WITH SEVERE TURB. VIOLENT UPDRAFTS AND DOWNDRAFTS CAUSED MY ALT TO VARY PLUS/MINUS 1000 FT AND HDG TO VARY PLUS/MINUS 30 DEGS (BOTH CLRLY IN VIOLATION OF MY CLRNC). I SLOWED TO MANEUVERING SPD AND STRUGGLED TO MAINTAIN ATTITUDE AND AIRSPD WITHOUT TEARING THE WINGS OFF THE PLANE. ZMP INSISTED A COUPLE TIMES THAT I DSND IMMEDIATELY TO 5000 DUE TO FOLLOWING TFC. I TOLD THEM I WAS UNABLE TO DO THIS BECAUSE OF THE ROUGH AIR. AT ONE POINT; AN UPDRAFT TOOK ME TO 7500. THIS TURB AND ALT VARIATIONS LASTED A TOTAL OF 10-15 MINS BEFORE LEAVING THE TURB AND RE-ENTERING VMC. I CLRLY SHOULD NEVER HAVE ATTEMPTED TO CROSS THE FRONT GIVEN THE WX BRIEFING; THE KNOWN PRESENCE OF 2 LARGE CELLS ON EITHER SIDE OF ME; AND THE KNOWN LIMITATIONS OF A STORMSCOPE. ALTHOUGH THERE WAS NO LIGHTNING OR RAIN IN THE HOLE; THE TURB COULD EASILY HAVE DESTROYED THE PLANE. AFTER SEEING SUCH A CONTINUOUS LINE OF STORMS FROM E OF PIR ALL THE WAY DOWN TO E OF ONL; I SHOULD HAVE DETERMINED THAT I WASN'T GOING TO BE ABLE TO GO FAR ENOUGH S TO GET ALL THE WAY AROUND ALL THE STORMS AND SHOULD HAVE LANDED AT ONL. THE OBVIOUS LESSONS ARE: DON'T PUSH KNOWN BAD WX AND DON'T USE A STORMSCOPE TO PENETRATE A LINE OF STORMS.