Daniel, when you shine a torch onto an object you illuminate that object and not what is behind it (that is why shadows are comparatively dark :( ). Furthermore, the shadow cast by the object (aka radar blind spot) grows relative to the inverse distance of the object from the torch.The pilots could have conceivably flown through what appeared to be a small storm only to be confronted by a much larger one behind it. Now factor in super-cooled water freezing on contact with the pitot tubes, instrument discontinuity, autopilot disengagement, severe turbulence and pitch darkness...