They may appear similar in many ways, but snow, ice, and hail are different not only in how they look and feel but also in how they are formed. We examine the main differences between them.

Water in its various frozen forms develops both in the atmosphere and on the ground, with many factors involved in its formation. As a result, it can be difficult to distinguish between the different ice formations and understand how they develop.

Readers living in Scandinavian countries, Canada, Russia, and other regions close to the Arctic Circle will probably find this subject very amusing. There are many readers, though, who experience the phenomena of ice, hail, and snow very seldom (if at all).

This article examines what ice, snow, and hail are and how they differ from each other by looking at how they are formed and defining their characteristics and structure.

It also takes a look at other frozen forms of water and related phenomena, and how they relate to ice, snow, or hail. This includes well-known formations like sleet, freezing rain, graupel, rime, and frost.

Before getting into further detail about how it is formed and its characteristics, one first needs to describe what precisely ice is:

Ice Definition​​​​​​​​​

Ice is the umbrella term used to describe all forms of water in its solid state. When water in its liquid state is exposed to temperatures below freezing point for long enough, it turns into the hard, solid substance we know as ice.

Apart from its hard, solid nature, ice also differs from liquid water in several other ways.

Technically, ice still consists of two hydrogen atoms combined with one oxygen atom, just like liquid water.

One important and sometimes overlooked difference between ice and water is the fact that ice has a lower density than water. This is a result of the orientation of the hydrogen atoms as the temperature is lowered, pushing the water molecules further apart as it freezes and ice is formed.

This decreased density of ice also makes it lighter than water. This is why ice objects always float on top of water. (Two examples are the icebergs floating  in the ocean, and the ice covering and floating on top of a pond or lake.) 

Another important feature of ice is that it expands as water freezes and turns to ice. This means ice occupies a larger volume of space than water, which can be a potential problem.

Water in the cracks of building materials like concrete or stone will expand when it freezes. This often leads to an expansion of the cracks in these materials, which can weaken them and cause structural instability and potential collapse.

Flooding in buildings due to burst pipes is common in regions experiencing long periods of temperatures below freezing point. As the water in the pipes freezes, it expands, causing many pipes to burst under the pressure.  

As with the other frozen forms of water discussed in this article, the composition and characteristics of ice are partly determined by how it was formed.

As earlier stated, ice is formed when water is turned from its liquid form to its solid form by being exposed to temperatures below freezing point.

There are various ways in which ice can be formed, both on the ground and in the atmosphere. There is no need to explain each one in detail, as most of these processes occur very much in the same way.

By using an example of ice forming on the ground and another of ice forming in the atmosphere, you will be able to get a much better understanding of ice formation in general.

On the ground, the formation of ice very often takes place in bodies of water (dams, ponds, and the ocean) due to a drop in atmospheric temperatures. This is often seasonal as well, coinciding with the colder winter months in many countries.

During these cold winter months, many countries in the Northern Hemisphere closer to the Arctic Circle start to experience temperatures well below freezing point. As the winter months arrive and temperatures start to plummet, smaller bodies of water (like ponds) are the first to turn into ice.

Larger bodies of water take much longer, but over time the surface water of larger lakes starts to ice over, and parts of smaller rivers stop flowing as the water turns into ice. 

A critical part of the Arctic’s seasonal cycle is the growth of its sea ice during the Northern Hemisphere’s winter months. As temperatures continue to drop, more of the Arctic Ocean freezes, causing the sea ice cover to expand significantly.

As much of the Arctic receives little or no sunlight during the winter months, temperatures drop very low. This allows the Arctic sea ice cover to expand to around 15 million km² (5.8 million square miles), normally reaching its maximum extent in March.

The formation of ice on such a large scale annually is vital for the regulation of the temperatures of the world’s oceans, as well as helping to control the climate on a global scale.

In the atmosphere within cloud systems, ice is also formed when water is turned into its solid state as a result of subzero temperatures, but the process through which it takes place is quite different.

In large cumulonimbus clouds, including those associated with supercell thunderstorms, strong vertical development can cause the clouds to reach well into the upper troposphere. This creates an ideal environment for the formation of ice.

These clouds normally contain a combination of powerful updrafts and downdrafts. As water vapor condenses into water droplets, it can be carried up higher into the clouds by updrafts.

At these heights, temperatures are well below freezing point, and many cloud droplets remain liquid in a supercooled state. When these droplets come into contact with a small piece of ice, they freeze onto it. The growing piece of ice may begin to fall before being carried upwards again by another strong updraft, where it collects more supercooled droplets and ice particles.

During this whole process, the ball of ice continues to grow in size until it becomes too heavy to stay in the air and falls to the ground, usually in the form of hail. (We will discuss hail in much more detail later on in the article.)

Freezing rain normally begins as snow high in the atmosphere. As the snow falls through a layer of warmer air, it melts and turns into raindrops. These drops then pass through a shallow layer of freezing air close to the ground, where they become supercooled but remain liquid.

When the supercooled raindrops strike the ground or another cold surface, they freeze almost instantly and form a layer of ice.

From just these two or three examples just described, it should become very clear that there are a wide variety of ways in which ice can be formed, both on the ground and in the atmosphere.

But, at the end of the day, ice is just ice, correct? No matter how they are formed, the end result is still the same…

Well, no, not exactly. When casually observed, all forms of ice may look the same, but if you took a closer look, you would notice some subtle but important differences.

What is even more important is that different forms of ice have characteristics that make them react differently to their environment. By just looking at a few examples, you will be able to understand why not all ice is “created equal.”  

Freshwater Ice:

This is probably the most common form of ice, as freshwater is the most abundant type of water found in our rivers, dams, lakes, reservoirs and households. It has the common characteristics of “normal” ice and also freezes consistently at temperatures below 32° Fahrenheit or 0° Celsius.

Sea Ice:

As the name suggests, sea ice is formed when ocean water is turned into ice due to a drop in temperature to below freezing point. But it is here where its characteristics differ from freshwater ice. Due to the amount of salt in seawater, sea ice takes much longer to form than freshwater ice. (Seawater gets denser as it cools down and sinks away from the surface.) The freezing point is also much lower at -1.8° Celsius (28.8° Fahrenheit), prolonging the formation of sea ice even further.

Glaze Ice:

When supercooled water drops from freezing rain hit a cold surface, they instantly form a thin, clear layer of ice with a very smooth surface. This is a particularly dangerous form of ice when formed on surfaces like roads and pavements. It is almost invisible to the naked eye and very smooth, making it very easy for motorists, pedestrians and cyclists to slip on.

Hail:

We already discussed hail in some detail and will do so in much more detail later on in this article. But as we have already seen, hail forms inside storm clouds when supercooled water droplets freeze onto small pieces of ice in the upper regions of the cloud, causing them to grow into hailstones.

These are just four examples of many variations of ice and the many forms it takes. Next time you see a piece of ice that didn’t come out of a refrigerator, remember “ice is never just ice”.

Like ice, one first needs a clear, concise definition of what precisely snow is before getting into further detail about how it is formed and its characteristics:

Snow Definition​​​​​​​​​

Snow is a collection of ice crystals that often form around tiny particles of pollen or dust as water vapour changes directly into ice in subzero temperatures in the atmosphere. When these ice crystals start clinging together, snowflakes are formed. As more crystals are added to a snowflake, it grows in size and weight until it becomes too heavy and starts falling to the ground as a result of the Earth’s gravity.

The most obvious difference between snow and ice can be found in the way they are structured. A snowflake is much lighter and more fragile than a similar volume of ice, which is much denser and almost solid in structure.

The soft and light structure of a snowflake (or any piece of snow) is a direct result of the fact that it is made up of a number of ice crystals with pockets of air trapped within them.

Each snowflake is hexagonal (six-sided) in shape, simply because it is mainly made up of hexagonal plates, prisms, and star-shaped (hexagonal) ice crystals.

It is important to note that, even though they might have the same shape, no two snowflakes are the same. Each one has unique properties.

Snowflakes are also white in color as they reflect all the colors in the color spectrum, which creates a white color when combined.

When viewed under magnification, a snowflake is made up of many different elements. Naturally, the multitude of ice crystals bound together takes centre stage when looking at the snowflake up close.

Among some of the other elements found in a snowflake are microscopic pieces of pollen and dust (around which many of the ice crystals are formed), as well as pockets of air containing oxygen, nitrogen, and a few other elements commonly found in atmospheric air. 

We are very familiar with snow falling from the sky in the form of snowflakes. Similar ice crystals can also form directly on objects near the ground in the form of hoar frost.

In the atmosphere

Ice crystals are formed when the temperature is already well below freezing point. Instead of forming microscopic water droplets, water vapour changes directly into ice around small particles of dust or pollen through a process called deposition, creating their unique hexagonal structure.

As the ice crystals start to come into contact and cling to each other, a snowflake is formed. Snowflakes retain their hexagonal shape as already explained, resulting in plenty of “air pockets” to be trapped inside the snowflake.

This allows a snowflake to be much lighter and less dense than a similarly sized ball of ice. The combination of the ice crystals’ structure and air pockets inside also allows snow to be easily transformed and compacted.

On the ground

Hoar frost is formed through an accumulation of ice crystals on the ground. Its formation is very similar to that of snowflakes in the atmosphere but takes place when water vapour comes into contact with objects at subzero temperatures.

On the ground, a variety of objects (lampposts, fences, leaves, branches, among others) may be exposed to subzero atmospheric temperatures, lowering their own temperatures to well below freezing point.

As humid air containing water vapour comes into contact with these cold objects, the water vapour changes directly into ice crystals. As these ice crystals accumulate on tree branches, fences, and other cold objects, hoar frost is formed.

Just like ice, snow also comes in a variety of different forms that are very often a result of the way in which they were formed. Just by looking at a few different examples, this will become very obvious.

Atmospheric Snow:

This is the most common form of snow and the one with which most of us are familiar. Ice crystals form in subzero temperatures in the atmosphere, start clinging together, and form snowflakes. After reaching a certain size and weight, the snowflakes fall to the ground as a result of the Earth’s gravitational force.

Hoar Frost:

This process also involves water vapor that is turned directly into ice crystals. Unlike ice crystals in the atmosphere, though, this process takes place on the ground where humid air comes in contact with objects with temperatures below freezing point, instantly allowing the water vapor in the air to be turned into ice crystals upon contact.

Sleet:

Sleet, which is often confused with freezing rain, starts as snow falling from the atmosphere. The snowflakes then pass through a warmer layer of air, causing them to melt and turn into water drops.

As the drops continue to fall, they may pass through another layer of subzero air, causing them to freeze into small ice pellets before reaching the ground. This differs from freezing rain, which remains liquid until it strikes the ground or another cold surface.

Graupel:

Sometimes referred to as “snow pellets”, graupel is formed when snow falls through an area of supercooled water droplets. Upon contact, the supercooled water freezes around the snowflake, coating it with rime and forming graupel.

This process alters the shape and appearance of the snowflake, often causing it to resemble hail. This is why graupel is sometimes referred to as “soft hail”. It is not nearly as solid as hail, however, and consists of a snow crystal coated in frozen water droplets, making it brittle and easy to crush.

These four examples provide plenty of proof that snow is formed in a variety of ways and comes in all shapes and sizes.

Hail has already been mentioned a few times during the course of this article (and in a few other articles on this website) and is essentially a subcategory of ice.

Yet, it differs from other forms of ice in so many ways and can have such a devastating impact on the environment that it deserves its own complete section.

As already mentioned, hail is essentially a form of ice. However, as you will soon discover, it differs so drastically in its structure and especially in the way it is formed that, in a way, it can be seen as an entirely different entity.  

Like ice and snow, one first needs a clear, concise definition of what precisely hail is before getting into further detail about how it is formed and its characteristics:

Hail Definition​​​​​​​​​

Hail consists of solid, layered balls of ice formed as water droplets are carried high into the atmosphere by updrafts in large cumulonimbus clouds, including those associated with supercell thunderstorms. At these high altitudes, they are exposed to temperatures well below freezing point, causing them to freeze and develop into hailstones.

As they are carried through additional updrafts and downdrafts in the storm clouds, additional layers are added until the hailstones grow too big to be kept in the air, and fall to the ground as a result of gravity.

Simply by looking at the structure of a hailstone, it should become clear how much it differs from the “normal” ice commonly formed on the ground.

Upon closer inspection, it quickly becomes clear that hailstones have a generally round but predominantly irregular shape. This differs dramatically from the structured hexagonal shape of snowflakes, which are made up of ice crystals.

This is a direct result of the fact that snowflakes are formed from hexagon-shaped ice crystals, which allow them to maintain this six-sided structure. Unlike snow, though, hail grows as supercooled water droplets freeze onto a small piece of ice and therefore has no fixed structure.

As supercooled water and other small ice particles attach themselves to a hailstone from different sides as it is carried through updrafts and downdrafts, a very irregularly shaped hailstone is formed. 

A hailstone is formed as supercooled water droplets and small ice particles build up around it in a storm cloud. As a result, the hailstone has a distinctly layered structure, very much like the layers of an onion. (This is clearly visible when looking at a cross-section of a hailstone.)

Another noticeable characteristic of hail is its translucent colour. It is not fully transparent because it consists of multiple layers of ice, with some impurities also finding their way into the hailstone’s structure.

The irregular shape of hailstones also hinders their transparency and contributes to the translucent color commonly associated with hail.

Hailstones also come in a variety of sizes, from as small as 5 millimetres (0.2 inches) to 15 centimetres (6 inches) in diameter. The size of a hailstone is determined by a variety of factors including the size of the storm cloud, the strength of updrafts and downdrafts, the amount of moisture in the air, and the vertical extent (height) of the cloud system.

Bigger hailstones can cause severe damage to buildings, vegetation, as well as motor vehicles. They can also cause serious injuries and even be fatal if human beings are struck. This is especially the case once hailstones reach the size of tennis balls, baseballs, or larger objects.

We already briefly touched on the formation of hail, but let’s take a more in-depth look at how a hailstone is formed.

Before looking at the formation process, let me just quickly dispel a myth that exists surrounding hail. It does not need to be cold and stormy on the ground in order for a hailstorm to occur. The weather can be perfectly tolerable or even slightly warm right before hail starts falling.

There are a few conditions, however, that need to be in place to ensure the formation of hail:

• A sufficient amount of moisture (water vapor) in the air.
• Strong updrafts.
• Storm clouds with a large vertical extent (distance from the cloud base to the upper region of the cloud), sometimes reaching up to 16 km (10 miles) in height
• Hail embryos in the form of very small pieces of soft ice or frozen raindrops sometimes referred to as graupel.
• Supercooled water droplets in the upper regions of the cloud system. 
• A relatively low freezing level.

Not all of these conditions need to be present for the formation of hail. Neither will the presence of each and every one of these conditions guarantee the formation of hail.

What it means is simply that the presence of these conditions provides the best possible environment for hail to form. Each one’s role will soon become clear.

As already mentioned, a strong cumulonimbus cloud, especially one associated with a supercell thunderstorm, forms the ideal environment for hail formation. These clouds contain strong updrafts as well as a large vertical buildup that is conducive to hail development.

As water vapor rises up into altitudes with lower temperatures, condensation takes place, and water droplets are formed. These water droplets get caught by updrafts and carried high into the atmosphere (sometimes 16-17 kilometres), where temperatures are well below freezing point and the water droplets are turned into ice.

As the updraft weakens or the frozen raindrop gets caught in a downdraft, it begins to fall through the cloud. As it falls, supercooled water droplets freeze onto it, adding to its size and weight, and a hailstone starts forming.

When the hailstone is caught by another strong updraft, it is carried back up into the cold upper atmosphere where the process repeats itself. This cycle will continue until the hailstone becomes too big and heavy for the cloud to hold it in the air, and the hailstone falls to the ground.

The size of the hailstones reaching the ground largely depends on the size and extent of the storm cloud itself, the strength of the updrafts, and the amount of moisture in the air.

Since hail is already a subcategory of ice, breaking it further down will be confusing. There are, however, two substances closely related to and often confused with hail. I already discussed them earlier in the article, but need to emphasise their differences from hail as they relate to their structure and formation:

Sleet:

Often mistaken for smaller hailstones, sleet is actually something completely different. The small frozen pellets that hit the ground begin as snow, which melts into water while falling through a warmer layer of air before freezing into ice pellets as it passes through a layer of subzero air.

Graupel: 

As previously mentioned, graupel is formed when snow falls through an area of supercooled water. Upon contact, the supercooled water freezes around the snowflake, coating it with rime and forming graupel. It may resemble hail, but is nothing more than ice-covered balls of snow that can be easily deformed and crushed.

If you managed to read through this whole article without your head spinning, congratulations! This topic can be very confusing and can lead to debate and disagreement.

For this very reason, I divided the article into separate sections covering ice, snow, and hail. Together, they cover the major forms of frozen water and water vapour.

Naturally, as you have seen, there are many more variations, mostly based on physical characteristics and formation. There is also a lot of overlap between the different categories, but all of them can essentially be placed in one of these three main categories.

I trust this article helped you to better understand the different forms of frozen water and cleared up any confusion you may have had about them.

Until next time, keep your eye on the weather!