Freezing rain hit the Côte-d'Or, making the ground extremely slippery and traffic almost impossible on the evening of Saturday January 4. But how can this well-known phenomenon cause such damage? Let's take stock.
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If you were in Côte-d'Or or in the north of Saône-et-Loire on the evening of Saturday January 4, it must have been difficult to leave your home. The ground was extremely slippery, making movement almost impossible. Portions of the A6 and A38 were closed for several hours. In the city, the sidewalks were transformed into real ice rinks.
One phenomenon is at the origin of all these disturbances: freezing rain. According to Météo-France, they are created when two air masses meet, one milder and the other colder. In some cases, the latter can persist near the ground. As they pass through this layer, the water drops cool while remaining in a liquid state.
An image of the freezing rains which hit the Côte-d'Or, like here in the Sombernon sector
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© Météo Côte-d’Or
This is called “supercooling”. In this state, the drops freeze instantly at the slightest contact with an obstacle. This creates a smooth, compact deposit of ice, more commonly known as sleet. This phenomenon is extremely rare, since it results from the sequence of several conditions.
A graph explaining the formation of freezing rain or “supercooled rain”
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© Météo France
The cold air must be trapped in the lower layers of the atmosphere, while at the same time the atmosphere cools at altitude. Ground temperatures should also not be too low to allow water droplets to remain liquid. It is therefore common to observe an episode of snow beforehand, followed by a generalized warm spell after these 'freezing rains'.
The ice formed contains very few air bubbles, which allows it to take on the color of the surface on which it rests. It is therefore difficult to detect with the naked eye. That's not all: the large quantity of ice that forms in a very short time makes traffic almost impossible.
On Saturday January 4, the Côte-d'Or prefecture advised people to limit travel and respect traffic restrictions. Despite these precautions, the prefecture recorded, in a press release, 51 material accidents, 16 bodily accidents causing 31 injuries, as well as a fatal accident on the A6, near the border with Saône-et-Loire. In addition, firefighters carried out 40 interventions.
