I don’t know about you, but the dogs and I love a cold and frosty morning walk. The cool fresh air hitting our faces, the sun starting to rise in the clear sky and getting invigorated for the day ahead.
There are lots of benefits to walking in the winter months for sure, but the flip side can be scraping the car of frost and/or ice before we can get anywhere.
Plus I am sure there are many gardeners out there that curse a big morning frost, especially when it comes late in the spring.
There are quick answers and longer answers to the differences between frost and ice and how they form. Let’s take a look at both.
The quick answer is that ice is water in its solid form that is reached when the water temperature is 0 ºC/32 ºF or below. Frost forms by water molecules in humid air becoming frozen on contact with cold surfaces.
What is Ice?
Ice is basically water in its solid form. Water reaches its freezing form at 0 ºC/32 ºF or below.
That is a quicker answer than when talking about frosts. here are some common types.
What Is Frost?
Frost is a coating of ice crystals that forms in humid conditions on cold surfaces.
When you get up on a cold morning do you look out at your car to see if you need to scrape the windscreen and determine if you’ll need to allow extra time before you set off?
The reason I got looking into this myself was because some mornings it can be below freezing yet the car is clear. And some mornings the temperature can be a couple of degrees above freezing yet there we are, having to make time to scrape away.
To work out frost we first need to look how dew and condensation are formed.
Dew and Condensation
Here in our temperate part of the world we are used to moist atmospheric, humid conditions. Water molecules in the air; water in its gas form.
Overnight, as the temperature drops, the ground/grass temperature drops too and cools the air around it, turning these gas water molecules into liquid form and producing that morning dew on the ground.
The same is true of condensation. If you have, say, a long hot shower you release steam, water vapour, around the room. The colder mirror surface turns this vapour back into liquid form on its surface. So you now can’t see yourself.
Now think of this process at much lower temperatures.
Air Frost
Air frost occurs when the temperature of the air, for at least 2 metres up, is below freezing, never mind the ground. This is where there really is no escape for those water molecules. You wake up and all is white: the garden, the car, even the roads. The water droplets in the air have formed frozen crystals over many objects.
Ground Frost
Sometimes known as grass frost, this occurs when the air temperature may be a little above freezing, yet the grass, trees, etc. have a coating of frost.
Some objects or materials are better at keeping in heat than others. Grass cools fast overnight and can drop below freezing even when the air just a couple of metres above it is above freezing. The grass cools that moist air around it, causes condensation, and turns it into ice crystals.
This is why you sometimes have to scrape your car though the thermometer says it is 1 or 2º C outside. Overnight your car roof and windscreen are losing their heat and getting none back in return.
That glass and metal material drops below freezing and freezes any moist air it comes into contact with.
This effect on the car normally needs no breeze or wind to cause that frosty type of ice. A breeze would keep the air around the surface of the car above freezing. Hence it is more common on those cold, still mornings.
Hoar Frost
Hoar frost is the ice crystalisation of the dew process. This is where all the grass has a layer of ice crystals on it, and the trees too, as if frozen in state.
A hoar frost occurs when dew would normally form but instead of collecting the water in liquid form it collects in frozen form on any cold object like grass, trees, flowers, or your car windscreen.
Mist As The Sun Rises
As I am out walking on that gorgeous frosty morning, the sun starts to rise. This is where the reverse starts to happen.
The sun rises and starts to warm the ground. The ice crystals start to turn very quickly from their solid state, through liquid state and into gas state as the air gets warmer.
A layer of mist starts to rise from the ground.
Why Doesn’t The Car Freeze When Parked Under Something?
You may be thinking then, why, when the air is still and cold and filled with moisture, does the car not freeze up overnight when under something or if using those screen covers?
Heat Radiation is the answer. The heat radiates away from the car or windscreen but the roof above or the object over the windscreen then radiates this back and keeps the surface above freezing.
Conclusion
The things I think about when I am out walking. Any given walk can make me want to know more hows and whys.
Frosty and icy days are magical to get outdoors in. Especially at sunrise. It gives me a mental boost for the day ahead.
Wintry dog walks come in so many varieties, they don’t always have to be wind and rain in the dark.