Narrative:

The flight 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 thunderstorms 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 north and south of the route. My plan was to use my stormscope to avoid both areas of storms before they grew together, or fly south of the system 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 south and east of onl, northeast. I was flying at 7000 ft MSL along the missouri with good ground contact, occasional light showers, and light to moderate turbulence. About 15 mi west of ynk on the 270 degree radial, the stormscope showed 2 clusters with about a 15 mi gap in between. I felt the gap was large enough to presume nothing worse than moderate turbulence. 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 descent to 5000 to stay below the bases and was told to report leaving 6000. It quicklyy became apparent that I would have to enter IMC to cross the front. I reported leaving 6000. After entering the clouds, I was hit with severe turbulence. Violent updrafts and downdrafts caused my altitude to vary plus/minus 1000 ft and heading to vary plus/minus 30 degrees (both clearly in violation of my clearance). I slowed to maneuvering speed and struggled to maintain attitude and airspeed without tearing the wings off the plane. ZMP insisted a couple times that I descend immediately to 5000 due to following traffic. I told them I was unable to do this because of the rough air. At one point, an updraft took me to 7500. This turbulence and altitude variations lasted a total of 10-15 mins before leaving the turbulence and re-entering VMC. I clearly 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 turbulence could easily have destroyed the plane. After seeing such a continuous line of storms from east of pir all the way down to east of onl, I should have determined that I wasn't going to be able to go far enough south 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.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSIONS ACCOUNT OF TSTM ACTIVITY.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.