That’s why bridges get colder and icier quicker. Black ice is very difficult to identify in the dark, and it can be harder to predict than snow is, Lauder said. “It’s a tricky one, because you can get it in a very isolated little pockets of cold, that’s not necessarily in the forecast, and it’s not obvious to people.” The agency says they won't always know where and when ice will form, because it’s based on a forecasting system. Waka Kotahi monitors the forecast, checking at 4pm the night before. Rachael Kelly/Stuff/Stuff Freezing fog and black ice make roading conditions treacherous in Winter.