I have had two experience with t-storms while flying. One time coming into DC, we had a T-storm directly ahead. Took us 10 minutes to go around it.
Flying from SF to Atlanta once, we went through a squall line over Alabama or Mississippi. There was lightning around but it didn't hit the plane. It was the worst turbulence I have felt. I was white knuckling it. The guy next to me flew a lot more and kept reading his book. When we landed in Atlanta, I saw on the CNN weather that there were tornadoes in that line of storms.