Snow can be defined as a type of atmospheric precipitation, a form of crystalline rain that occurs when a negative temperature is reached. At this temperature, the water drops turn into white and light flakes, the snow.
Several factors must be met in order to observe this weather phenomenon. And yes, negative temperatures are not enough... The formation of snow requires: the presence of water vapor, low temperatures and particles.
Let's go back to the beginning to understand how it is formed:
The water of lakes and oceans evaporates in a first time in contact with the heat. This water vapor rises into the atmosphere. The more this vapor rises, the more it is subjected to low temperatures and condenses in contact with clouds to form droplets. Within the clouds, the droplets will agglomerate on the particles present in the air, being microscopic like dust or sand. After that, the temperature comes into play and will determine the type of precipitation.
If the temperature of the cloud is above 0°C, then rain precipitation will follow.
However, if the temperature of the cloud is below the freezing point, below 0 °C, then the water freezes and ice crystals form around the particles. When the ice crystals become too heavy, they will break away from the clouds and fall towards the ground in the form of solid precipitation: snowflakes.
Like precipitation, snow can take different forms since the flakes are influenced by the air temperature before they fall on the ground. We can distinguish :
Dry snow: also known as "powder". It can be considered as the "perfect" snow for skiing. It usually falls when it is very cold in the mountains and does not contain liquid water. It is only made of crystals, it is very light and does not stick.
Frost: this is a type of snow that forms directly on the ground. Indeed, when the temperature is lower than 0 with a high rate of humidity, the water on the surface of the ground freezes and will form frost.
Wet snow: it is more frequent in the plains and appears when temperatures are slightly positive. It contains a little liquid water and sticks very easily. It is wet, heavy and if it accumulates, it can cause significant damage and disruptions to the various traffic routes.
Wet snow: as its name indicates, it is made up of a lot of water and can form at positive temperatures (1/3° C). It is very heavy, can be easily removed, but becomes dangerous, as it can easily turn into ice.
Freezing rain: In this case, the snowflakes first pass through a positive and then negative air mass which turns them into freezing rain which can be very dangerous.
We can distinguish different shapes of snow crystals.
In 1988, Nancy Knight, a research scientist at the National Center for Atmospheric Research in Colorado, spotted two flakes that were perfectly identical, both from a storm in Wisconsin.
The American continent records an average of 105 snowstorms per winter.
The larger snowflake, measuring 38 cm by 20 cm in height, was observed in January 1887 at Fort Keogh, Montana.
The record for the most snowfall in one day was set in Italy, in the village of Capracotta. In March 2015, 2.5 m of snow fell in one and a half days, an average of 13 cm/hour.