Published on: 3.2.2020

Information produced by Finnish Environment Institute

Where does the snow go in spring?

Lumi sulaa männyn neulasista.

The snow cover can disappear quickly in spring. Does the snow evaporate, or is it melted by rain? Does newly fallen snow speed up the melting of older layers?

Snow can start disappearing very quickly in spring. While people have held many different ideas about where the snow goes, the truth is relatively simple.

Even if the weather were warm and the washing dried quickly on the line, snow does not evaporate into the atmosphere, at least not on a large scale. Direct evaporation only accounts for a few per cent of the disappearing of snow during spring.

Evaporation of snow mostly occurs in sunny weather when the air temperature is a few degrees above or below zero. If the temperature rises above +5 degrees or the air is humid, water vapour pressure in the air increases to a point where the vapour condenses on the snow surface.

Rather than washing the snow away, rain mostly saturates it with water. According to an old Finnish saying, new snow is the death of old snow, but this is not actually true. A snowstorm in spring is more likely to slow down the snow melt, as it covers the old snow with a clean new layer that is highly reflective.

As a matter of fact, the disappearance of snow in spring is mostly due to nothing more dramatic than warmer air causing the snow to melt into water. Some of the meltwater is infiltrated into the ground, while the rest runs into ditches and flows into rivers and lakes. The rest evaporates from snow-free patches appearing in the snow layer.

Image: © Riitta Weijola, Vastavalo