"It sounds like the plane iced when they flew through the cell. They thought at first it was light to moderate icing. But then it sounds like it got really severe."

"The plane can become almost uncontrollable.... They couldn’t recover from it, and they crashed.... This, to me, is just a textbook example of exactly what we’re taught when we’re pilots, and that is, don’t fly through thunderstorms, because you just don’t know their severity."

Said Daniel Bubb, a former pilot who now teaches at the University of Nevada, quoted in "What Caused a Jet to Dive Nose First Into the Ground? Ice, experts said, can change the shape of a plane’s wing, disrupting its aerodynamics" (NYT).