Black ice, sometimes called clear ice, is a thin coating of glaze ice on a surface, especially on streets. The ice itself is not black, but visually transparent, allowing the often black road below to be seen through it. Black ice is highly transparent and thus difficult to see compared with snow, frozen slush, or thicker ice layers. It is most prevalent during the early morning hours, especially after snowmelt on the roadways has a chance to refreeze overnight when the temperature drops below freezing. Black ice forms without creating bubbles, which allows it to blend in with any surface it forms over. It is dangerous precisely because its hard to detect in advance. Black ice can be very dangerous, so its important to know what it is and how to react if you have an encounter. It can lead to hazardous driving conditions, and roadways become very slippery when black ice forms, leading to an increased risk of car accidents. Black ice is most likely to form when there is a sudden temperature drop, such as in the early morning and evening hours. Common problem areas include bridges, overpasses, and shaded areas of the road.