What does rain do to snow? The connection between rain and snow is quite fascinating and definitely deserves your attention.
Both snow and rain are a form of precipitation and together they shape the environment and influence various aspects of the world.
Comprehending the interplay between precipitation in the form of rain and snow can provide insight into the intricate mechanisms of atmospheric conditions and the ecological milieu.
So, what does freezing rain do to snow?
Freezing rain can compact snow, creating a harder layer of snow on top, which can cause unsafe situations, potentially disrupting transit and endangering pedestrians.
What Does Rain Do to Snow?
Because the upper atmosphere is so cold, it is common for precipitation to begin as falling snow.
It descends through layers of warmer air causing the snowflakes to melt into liquid drops.
In certain conditions, the drops pass through another cold air layer and reach the earth supercooled as freezing rain.
Although instances of freezing rain or ice storms are increasing, they remain rare because they form in highly specific conditions.
Due to cold air damming or CAD, a low-level cold air mass gets physically trapped, typically by mountains.
The phenomenon is also known as the ‘wedge’ because cold air is wedged in topographically.
It has produced some of the worst ice storms ever known across the eastern United States because of the Appalachian Mountains.
More about How Freezing Rain Forms
Supercooled droplets occur in clouds all the time in rain formation but water droplets can only freeze and form snow around an ice nucleus.
Rain begins as snow as usual, but this cloud snow doesn’t reach the ground but melts, losing its nucleus as it travels through layers above zero degrees.
If it does meet a layer of sub-zero air near ground level, its temperature falls below zero but it cannot refreeze into a snowflake.
Fact: When water vapor in the air condenses into ice crystals, snowflakes form, resulting from these ice crystals coming together and sticking to one another to form their distinctive patterns.
The Interaction between Freezing Rain and Snow
As a liquid, the supercooled drops spread out as a layer on any surface close or below freezing it meets and instantly freezes forming ice.
The process is repeating, so many ice layers form one on top of each other as a glaze.
When rain above zero degrees forms on snow, the warmer temperature melts the uppermost layers of the snowpack to form a rain crust that refreezes if temperatures fall.
However, when the rain is at or around freezing instead of melting the crust, seeded by the ice in the snow, the drops of freezing rain instantly crystallize.
Physical Transformations of Snow Due to Freezing Rain
Once a snowflake makes it through the atmosphere to the ground in freezing conditions, it settles in layers in a snowpack.
The character of any snowpack changes according to the conditions around it and what and how much is added to it.
The combination factors dictate how long the snowpack lasts.
Varying conditions, such as temperature and subsequent precipitation, create layers in a snowpack.
A freezing rain event adds layers as ice.
Both ice and distinctive snow layers can render snowpacks unstable although where there are layers of ice and snow lying one above the other, the risk of instability is higher.
The Role of Ice Crust Formation
An ice crust is a type of snowpack crust that makes up the top few layers.
It will stay stable and remain on top for as long as conditions around the snowpack stay the same.
Usually, conditions change and this ice layer may go through several cycles of melting and refreezing forming a melt/freeze crust of irregular ice crystals.
It continues until another layer of precipitation covers it to compress it towards the center of the snowpack.
It will last for as long as the conditions at the center remain stable or it evaporates away as a melting sun crust in rising temperatures.
Fact: Each snowflake is different because it forms and falls under its own unique set of environmental variables, including temperature and humidity.
Snow Compaction and Density Changes
The longer a snowpack lasts, the more time it has to compact into a thinner layer.
The more layers it has above it, the more heat and weight there is, creating greater pressure increasing the compression rate.
The process forces all the matter in the layer closer together, displacing the air as a result the layer’s density increases.
Fresh snow is full of air and so has a low density of 100 kg m3.
However, the density of compacted snow, although still less than that of ice, can be 400 kg m3 transforming it into solid ice as in a glacier.
Effects on Snow Texture and Structure
With compression, the texture and structure of the grains of snow change.
They undergo sintering (frittage), as water vapor is deposited to form links between them.
Atoms diffuse across the particle boundaries fusing the grains into one piece.
This is when a solid rounded mass forms using heat and pressure without liquefaction.
It may also lead to other effects, including the following:
Decreased Snow Porosity
There is indeed ongoing research into the properties of snow.
But, it is accepted that because the three states of water are present in wet snow, their interactions with the solids reveal it to be a ‘complex porous medium’.
Wet snow often has a porosity of around 50% although liquid water fills less than 10% of the total pore volume and the rest is ice.
There are always pockets where the porosity is higher or lower because liquid water, rain, never penetrates through a snowpack evenly.
The increasing liquid water fills the pore spaces and the snow decreases accordingly in its porosity.
Reduction in Insulating Properties
Snow has long been recognized for its excellent insulating properties that are largely the result of it being so porous but in the rain it decreases as the structure becomes saturated.
Snowpacks form pockets of warmer air where it meets the ground. These alone trigger constant changes in its structure.
Snow acts like an insulation blanket, preventing the ground from freezing which will lock in the carbon and methane.
Both of these are needed for chemical exchanges between the ground and the atmosphere and as well as impact the movement of water.
What’s more, snow’s effectiveness as an insulator is enhanced because it is also highly reflective.
Environmental Implications of Freezing Rain on Snow
Snow reflects back an enormous amount of sunlight, sending the unwanted heat back into space.
Therefore, the amount of snow there is has an enormous impact on how the Earth’s surface heats up or cools down.
However, with global warming, ice caps are melting and freezing rain events are increasing, causing serious effects on ecosystems and water resources.
Fact: Snow's porous nature gives it great insulating capabilities, and the trapped air acts as a heat sink, keeping temperatures roughly constant under the snow.
Impacts of Rain on Ecosystems
Freezing rain on snow can have a direct impact on ecosystems in many ways.
For instance:
Challenges for Vegetation and Wildlife
With global warming we are told to expect a warmer, wetter climate. More rain is forecast and all life on earth will have to adjust.
The ice caps, compacted snow, are melting rapidly adding water to the atmosphere at an alarming rate.
There will be higher humidity and torrential downpours.
Changes in Soil Temperature and Moisture
Without the protection of snow, the planet will warm and soil temperatures increase until its moisture is lost and dries out.
Predictions are that global warming will see huge new regions of desert, whilst the equatorial regions become more saturated, with obvious implications for food production and population settlement.
Effects on Water Resources
With more rain and less snow, it not only makes the ground lose heat when the rainwater freezes but it also forms an ice seal over the surface of the land.
Unable to penetrate the soil, the water runs off taking whatever course it can towards lower ground.
Inevitably, the rainwater will pool creating new areas of flooding adding volume to freshwater tables, oceans with rivers and streams flowing faster.
As well as predictions of vast new areas of desert, there will be new coastlines and vast areas of saturated land that are unsuitable for agriculture or settlement.
Fact: The structure, water content, and texture of snow all contribute to its categorization into distinct subtypes, including dry powder, wet snow, slush, etc.
Takeaway
What does rain do to snow?
Rain affects snow in several ways, such as compacting the snow, creating harder layers on top, and causing potentially unsafe conditions.
Freezing rain can cause the snow to undergo various physical transformations as well.
Environmental implications of freezing rain on snow include impacts on ecosystems, challenges for vegetation and wildlife, and so on.
