Narrative:

Initial cruise altitude was FL370. After burning down we ascended to FL390 and shortly thereafter started maneuvering through a group of cells. We had just cleared a significant echo and turned southeast to clear a secondary line. We were upwind of the second line and downwind of the cell we had just passed. Winds were from the west at 60+ KTS as we were deviating to the southeast. We were clear of the echo; but as we were entering a cloud bank upwind of the storm we encountered the upper end of moderate turbulence just after a surge in airspeed/mach which ran up to .81-.82 rapidly. Then of course the rapid deceleration after a large thrust level change which put us into the stick shaker limit. Associated with the initial mach surge it felt like a mountain wave action followed by an updraft or some type of combination which gave us a significant toss. I quickly asked for FL370 followed rapidly by; 'we have to have it;' and then told the controller that we were going. The PF had his hands full with the fluctuations and was doing a good job but I wanted him to have some extra maneuvering room to FL370 so I forced the descent. The controller said he had traffic and asked if we were declaring an emergency and I said yes. I am not sure if he had to move the guy or not. The event was short lived and we broke out in the clear and called the traffic that he was referring to. We obviously got too close to the cell and probably did not give enough of a buffer from the echo. In retrospect; I must have been more concerned about being downwind of the other cell to give this one enough respect. After we got back on course and looking back visually at the line it was painfully obvious that this was a very significant thunderstorm. I felt pretty stupid.

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Original NASA ASRS Text

Title: B737 FLT CREW OPERATING IN THE VICINITY OF TSTMS ENCOUNTERED SIGNIFICANT AIRSPEED LOSS; DESCENDED; THEN DECLARED EMER TO OBTAIN DESCENT CLRNC.

Narrative: INITIAL CRUISE ALT WAS FL370. AFTER BURNING DOWN WE ASCENDED TO FL390 AND SHORTLY THEREAFTER STARTED MANEUVERING THROUGH A GROUP OF CELLS. WE HAD JUST CLRED A SIGNIFICANT ECHO AND TURNED SE TO CLR A SECONDARY LINE. WE WERE UPWIND OF THE SECOND LINE AND DOWNWIND OF THE CELL WE HAD JUST PASSED. WINDS WERE FROM THE W AT 60+ KTS AS WE WERE DEVIATING TO THE SE. WE WERE CLR OF THE ECHO; BUT AS WE WERE ENTERING A CLOUD BANK UPWIND OF THE STORM WE ENCOUNTERED THE UPPER END OF MODERATE TURB JUST AFTER A SURGE IN AIRSPD/MACH WHICH RAN UP TO .81-.82 RAPIDLY. THEN OF COURSE THE RAPID DECELERATION AFTER A LARGE THRUST LEVEL CHANGE WHICH PUT US INTO THE STICK SHAKER LIMIT. ASSOCIATED WITH THE INITIAL MACH SURGE IT FELT LIKE A MOUNTAIN WAVE ACTION FOLLOWED BY AN UPDRAFT OR SOME TYPE OF COMBINATION WHICH GAVE US A SIGNIFICANT TOSS. I QUICKLY ASKED FOR FL370 FOLLOWED RAPIDLY BY; 'WE HAVE TO HAVE IT;' AND THEN TOLD THE CTLR THAT WE WERE GOING. THE PF HAD HIS HANDS FULL WITH THE FLUCTUATIONS AND WAS DOING A GOOD JOB BUT I WANTED HIM TO HAVE SOME EXTRA MANEUVERING ROOM TO FL370 SO I FORCED THE DSCNT. THE CTLR SAID HE HAD TFC AND ASKED IF WE WERE DECLARING AN EMER AND I SAID YES. I AM NOT SURE IF HE HAD TO MOVE THE GUY OR NOT. THE EVENT WAS SHORT LIVED AND WE BROKE OUT IN THE CLR AND CALLED THE TFC THAT HE WAS REFERRING TO. WE OBVIOUSLY GOT TOO CLOSE TO THE CELL AND PROBABLY DID NOT GIVE ENOUGH OF A BUFFER FROM THE ECHO. IN RETROSPECT; I MUST HAVE BEEN MORE CONCERNED ABOUT BEING DOWNWIND OF THE OTHER CELL TO GIVE THIS ONE ENOUGH RESPECT. AFTER WE GOT BACK ON COURSE AND LOOKING BACK VISUALLY AT THE LINE IT WAS PAINFULLY OBVIOUS THAT THIS WAS A VERY SIGNIFICANT TSTM. I FELT PRETTY STUPID.

Data retrieved from NASA's ASRS site as of January 2009 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.