One of the problems is that some atmospheric processes are still not understood. One is the way super-cooled water behaves just in simple freezing on nucleation particles. (
http://www.pnas.org/content/99/25/15873.full.pdf ). So there are bound to be the occasional surprises with high velocity flight through this kind of weather. I would expect work is going on researching what weather conditions caused the problem, such as size of droplets, density of droplets, temperature etc.