It’s the nightmare of many: You’re sitting in the car and suddenly it becomes icy smooth. Many call the phenomenon Blitzeis, but how does it occur? And is it the same as freezing rain?
The term Blitzeis hasn’t been around for that long. It was not until the 1990s that the term “blizzard” came into use for this weather phenomenon. Until then, Blitzeis was simply called “freezing rain” and “black ice”.
This already says what black ice is: rain that hits a surface that has been exposed to severe frost for a long time and has cooled down accordingly. Therefore, as soon as the rain hits the ground, it freezes. This happens suddenly, from now on. Hence the term Blitzeis.
Very pure raindrops fall through clean and very cold air. The cold is not enough that the rain is already freezing. However, the drops have already cooled down extremely, but are still liquid. If they then fall on the cold asphalt, they come into contact with dirt and dust. These so-called “crystallization particles” cause ice crystals to form. The freezing water forms a hard, glassy, ??coherent layer of ice within seconds.
However, it does not necessarily have to be rain, which then leads to dangerous ice. Black ice can also form due to freezing fog or even due to freezing air humidity.
The risk of black ice is particularly high in shady places, such as in forests or on bridges. Sometimes traffic signs already indicate this danger. The treacherous thing about freezing wet: the layer of ice is hardly recognizable and appears suddenly. However, fog and hoarfrost on trees can be indications that black ice is imminent.
In any case, the prerequisite for the freezing wetness is that the temperatures on the ground and near the ground are below zero degrees, while a warmer layer of air moves above it, which is accompanied by rain or fog.
If, on the other hand, the precipitation already falls in the form of grains of ice, it is referred to as freezing rain. Meteorologists call this “freezing rain”. This form of precipitation creates an irregular sheet of ice on the ground. This usually occurs in the transition area between rain and snowfall, for example with sleet or rain and hail. In black ice, on the other hand, the raindrops falling on the road freeze evenly. The result: a mirror-smooth ice surface that can often be mistaken for wet.
Because the phenomenon occurs so suddenly, all traffic is often paralyzed locally or over a large area. Cars, trains and planes can’t get any further. While in road traffic it is the slippery roadways that become dangerous when there is black ice, the railway has to contend with icy overhead lines. With planes, the problem is different again: the layer of ice makes the plane heavier and the airfoil profile changes. This reduces buoyancy. That is why the aircraft have to be de-iced before take-off.
The insidious thing about these weather phenomena is that they often occur very suddenly and only locally. They usually only last for a very short time and are therefore difficult to predict exactly.
