In the 3rd arrondissement of Lyon (Rhône), in Saint-Priest or Villefranche-sur-Saône, very localized snow showers were observed last week.
A phenomenon all the more astonishing that no rain cloud was on the horizon.
This event is well known to scientists, who call this white shower industrial snow.
“This snow appears when there is a combination of a winter anticyclone associated with low clouds trapped at high pressure and the presence of a factory that will discharge polluting particles.
The latter will serve as a nucleus for condensation and freezing of the water vapor and crystals will form from the particles then fall to the ground”, explains Christelle Robert, forecaster at Météo France.
Sometimes up to 30 cm on the ground
Most of the time, this layer of snow does not exceed 2 or 3 cm on the ground.
“But sometimes there are 30 cm because of significant human pollution.
We were able to see it near the Cattenom nuclear power plant in Moselle, or near road tolls, ”reports Alexandre Thomasson, who works at Atmo Auvergne-Rhône-Alpes, the air pollution monitoring agency in the region.
The latter ensures that the snow “does not seem dangerous”.
“By extrapolating, we could even say that these pollution particles that fall to the ground are no longer in the air to be breathed.
But with the thaw, they go up, ”adds Alexandre Thomasson.
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According to Atmo, other showers could “occur in the coming days, thanks to favorable conditions for the accumulation of particles and weather conditions conducive to this phenomenon”.