A CRJ-900 flight crew erred in their judgment regarding cell avoidance when circumnavigating a line of thunderstorms. Their escape maneuver took them into a cell where they encountered severe turbulence and lost 2;000 FT of altitude.

Narrative

Cruising at FL350 and approaching a line of thunderstorms I requested and received a clearance to climb to 37;000 FT because it looked like we could possibly climb over them. As we got closer; I could see that we would not be able to cross the line at FL370 so; after looking at the line; I elected to deviate more to the right of course thinking that this was the best path around. The new intended flight path would have taken us to the right of the towering thunderstorm cloud. There was still weather to the right but it looked like we would be able to clear the cell in front of us and then turn back to the left to get on course. As we approached the cell we realized that the intended flight path was not going to get us around the cell. It appeared that more weather was to the right of the cell that was not visible until this moment. I elected to make an immediate left turn and try to go around the left side of the cell where there was blue sky. As I started the turn; I could see that it would not be possible to complete the turn without going into the edge of the cell we were trying to avoid. During the turn; we entered the cell and experienced severe turbulence. Due to the sharp changes in wind speed and direction; the airspeed indicator tape was racing up and down. My goal at this point was to pay attention to airspeed and ride the turbulence out while I tried to complete about a 100 degree turn to the left to get us out of the cloud. With the airspeed going up and down very fast; the stick shaker did activate. During this time (which I would estimate at about 20-30 seconds in the cloud) the altitude went from FL370 to FL350. ATC did not mention any altitude deviations to us and I promptly corrected and climbed back to FL370.