Glaze ice

Scary stuff if you fly into it. The twig has nodules which were being hit by tiny droplets of river water in freezing air. The droplets do something remarkable. On impact a small section freezes, thus releasing a tiny amount of latent heat, the remaining supercooled liquid spreads or flows then freezes. This process continues as long as you like.....unless you happen to be flying a helicopter or fixed wing aircraft without a de-icing facility. 
Some of my scarier moments have involved glaze ice. It turns a huge whirling helicopter into a lollipop; the blades lose lift, the aircraft gets heavier and pretty soon the aerodynamic forces you depend on break down and you surrender to gravity - unless you can land quickly. 
In January 1979 a dozen of us were flying, in formation, across the Skagerrak from Denmark to Norway, half way across we encountered heavy precipitation, ice started to form. By the time we got onto a field in Norway the aircraft were coated in glaze ice and we were all rather nervous! 
Respect ice, especially if it's damn cold and then starts drizzling, you and your car will become the new Torville & Dean. 

Extra - Happy as pig in the proverbial. Outside air temperature 2ºC, warm sunlight on her back and she doesn't give a hoot. Taken from 40 metres away.