Snow on wings.
Just read the German accident report of the Manchester United crash at Munich. They failed to take off because of snow on the WINGS, nothing to do with slush building up in front of the WHEELS, other aircraft were taking off on the same surface, but with WINGS de-iced. If you have a problem reading your fuselage registration, have a discussion about wing de-icing, and live to tell the tale. Chug-a-lug.