Why is the snow not sticking? Ice and snow can indeed create difficult driving conditions as winter approaches.
But, the fascinating thing is that snow does not always stick to the road surface. And that is the case even when the temperature outside is below freezing.
Definitely, there are different factors at play, and drivers need to know about them to prepare for winter driving conditions.
So, why is the snow not sticking to the road?
The snow may not stick to the road because of the amount of moisture in the snow, the temperature of the road surface, and various other factors.
Why is the Snow Not Sticking?
There are several reasons why snow doesn’t stick and they are all related to temperature.
For instance, the temperature of the ground could be greater than 2oC and higher than the ambient temperature causing the snowflake to melt on contact.
Similarly, it may not stick because the ground surface is too wet.
This brings us to another question, “Does snow stick better to wet or dry ground?”
Let’s dig deeper into the details to find answers to these pressing questions.
Fact: Warming the road surface with sunlight, car exhaust, or subterranean utilities can stop snow from sticking.
Effects of Freezing Point of Water on Snow Sticking
Snowflakes form high in the atmosphere when the temperature is at or below freezing point, 0oC.
As the ice crystal forms and attract moisture, the snowflake becomes heavy and falls.
It will stay frozen for as long as the temperatures on the way down stay at or below freezing.
When they don’t, the snowflake melts, reaching the ground as sleet or rain.
When temperatures stay at or near freezing all the way down, the snowflake remains intact and reaches ground level where it will stick.
This is especially the case if the temperature of the surfaces it meets is also at or below freezing point.
Effect of Ground Temperature vs. Air Temperature on Snow Not Sticking
In the atmosphere, the surrounding temperature not only dictates if a water droplet will freeze but also what form it will take and its texture.
Snow that makes it to ground level is affected by air temperature and the temperature of the surface it eventually meets.
Even though the air temperature may be at or near freezing, where the surface temperature is greater than the freezing point of water, the snow doesn’t stick.
We see this effect when sidewalks, which are good at holding onto their heat, have no snow but their grassy verges being colder are covered in snowflakes.
Effect of Wet Ground on How Snow Sticks to the Surface
Snowflakes vary according to temperature and therefore come in different shapes and sizes.
Some have a better chance of sticking, but most kinds of snow are less likely to settle on wet ground.
This is because the ambient temperatures mean the liquid water on the ground is warmer than the ice crystals that make up the snowflakes.
This heat is transferred from the water to the ice causing the snowflake to melt.
If it continues to snow and the ambient temperature falls, say at night, the temperature of the water on the ground also falls, slowing or halting the melting process.
Fact: The amount of snow that accumulates on the road depends on its slope and gradient, and there may be less sticking snow on the road if the slope is steeper.
Effect of Dry Ground on How Snow Sticks to the Surface
Whether or not snow sticks on dry grounds depends on the structure of its crystals and the weather conditions it encounters at the surface level.
In areas with little moisture in the air, snowflakes won’t stick unless the temperatures are at or around freezing for the snow to accumulate faster than it melts.
Once on the ground, each snowflake begins to change.
Away from the clouds, they struggle to keep the moisture needed to maintain their structure.
Their crystal arms break away leaving the snowflake more rounded. Under gravity or blown by winds, they are compressed into layers forming snowpack.
Snow Characteristics Determining How it Sticks to the Ground
Generally, snow can be wet or dry.
Wet snow occurs when temperatures are just above freezing.
The edges of the flakes have begun melting which makes them sticky and more likely to adhere to cold surfaces at ground level.
The snowflakes also stick to each other and accumulate.
Each flake may melt and refreeze as it responds to changes in temperatures so the snow’s characteristics change over time.
Dry snow is powdery containing more air and less water than wet snow. It is therefore lighter but less sticky.
Although it accumulates, it will stay light and fluffy because there is less compression.
Why Doesn’t Snow Stick to Roads?
When snow is dry, the flakes do not stick together and a wind blows the snow into drifts.
Heavy wet snow tends to stay where it is and ice forms on top as a crust as temperatures rise and fall.
But, both kinds of snow produce hazardous driving conditions.
And many factors can have an impact here, such as:
- Road material and heat retention
- Road maintenance and snow removal
- Traffic Impact
Road Material and Heat Retention
There is ongoing research into the best thermal materials to use for highways and pavements in order to manage the urban heat island effect although the principles also apply to managing snowfall.
It is well known that asphalt absorbs and stores more heat than natural surfaces but it also stores more than concrete which can be up to 10oC cooler.
It is because black asphalt absorbs more of the sun’s rays. Having absorbed more, it can hold onto it longer.
Concrete being lighter in color reflects solar heat, absorbs less and releases faster, which affects how the snow sticks to the ground.
Road Maintenance and Snow Removal
For now, keeping roads free of snow means physically or chemically removing it after it has settled rather than preventing it from settling.
Salting and De-icing
Salting to de-ice roadways and pavements lowers the melting of the water and prevents it re-freezing.
The most widely used salt is common sodium chloride and there are growing concerns about how its widespread use is impacting the environment.
However, it is important to bear in mind that salting has a negligible impact on heavy snowfall.
It needs to be moved mechanically with a snowplow or snow blower depending on the size of the area and whether the snow is heavy and wet or powdery.
Traffic Impact
All precipitation has implications for traffic although blinding snow can bring it to stand still.
There are processes at work to determine whether or not it will stick.
Vehicles Compressing Snow
The weight of the vehicles compresses the snow, breaking the crystals down into a watery mush that is forced outwards forming ridges.
If temperatures fall the slush refreezes to ice which is just as hazardous.
Heat Generation from Tires
In light snow falls, friction from a vehicle’s tires creates sufficient heat to warm the tire rut and melt any snow in it.
This is why it does not stick to the road.
Fact: If traffic is heavy and the snow stays light, the repeated process and keep a highway open and driveable.
Implications of Snow for Transportation and Public Safety
Snow has always had implications for transportation and public safety.
Heavy snow makes it dangerous to move people and goods around. It disrupts delivery chains and has the potential to trigger panic buying.
Climate change models predict that warmer sea temperatures will result in less snowfall and more rain overall.
But, areas that do get it will see snow in huge volumes that consequently take longer to melt.
To keep roads open we need to change how we build them, and many researchers are already working in that regard.
Fact: Norwegian and Bulgarian researchers are investigating the effects of frost insulation on roads and finding a new synthetic polymer with thermo-physical properties.
Takeaway
Why is the snow not sticking? Several things contribute to snow falling to the ground but not sticking.
For snow to adhere to a road, the temperature of the road surface must be below freezing.
The snow may melt on contact if the road surface is warmer than normal due to residual heat or aggressive de-icing measures.
The snow’s moisture level also has a role in how well it sticks to the pavement.
Knowing these dynamics might assist drivers in better preparing for winter driving conditions by explaining why snow may not stick to the ground.
