What are hailstones and how are they made?

What are hailstones and how are they made?

The simple science twins are back to answer more of your questions; this one is all about hailstones and it comes in from five year old Matthew who can sometimes be found over on Office Mum’s blog. Matthew would like to know…

What are hailstones and how are they made?


What are hailstones?

Hailstones are small lumps of ice that form in the clouds and fall to the ground when their size reaches 5 mm in diameter, or larger.

They begin as water droplets that freeze in the clouds.

How are they made?

Hailstones are made in certain kinds of clouds, called CULUMONIMBUS. These are thunder clouds and if the cloud is large enough and the winds are strong enough, hailstones can be formed.

Firstly, the cloud contains tiny droplets of water. Under the right conditions, these droplets are blow to the top of the cloud by strong winds, called UP-DRAFTS. The temperatures at the top of the cloud are a lot lower than at the bottom so the water droplets freeze rapidly. Then they can be caught by winds, called DOWN-DRAFTS that carry the frozen droplet back down to the lower part of the cloud. It gets lifted again, by another up-draft and combines with another droplet of water, which freezes, forming a larger lump of ice.

Every time it travels up to the top of the cloud it merges with more droplets and gets larger, freezing in layers, until eventually it is too big and heavy to stay in the cloud and it falls to the ground as hail.

Hailstones usually fall once they are larger than 5 mm in diameter.

The size of the hailstones depends on the up-drafts and down-drafts and the general weather conditions. When the up-drafts become stronger the thunder clouds grow taller, allowing the droplets to be carried higher into colder temperatures. This usually leads to larger hailstones.

The largest hailstone ever recorded was 20 cm in diameter and weighed 0.88 kg. It fell in Vivian, South Dakota, USA on July 23rd, 2010.

What is the difference between snow and hailstones?

Hailstones are made up of layers of frozen ice whereas snow is a symmetrical crystal of ice, usually a snowflake.

Hailstones are much heavier than snowflakes and fall at a greater speed.

Snow is usually formed during the colder months of the year, in Winter or Spring whereas hailstones can be made at any time of the year. That is why we sometimes get them in the Summer months.


Thanks so much to Matthew for sending in this great question. If you have a question that you’d like the simple science twins to answer, send it in to me at drhowsciencewows@gmail.com or leave it in the comments below.


#FunFriday – Exploring Clouds

What are Clouds?

photo credit: Theophilos via photopin cc

Clouds are made up of tiny drops of water or ice crystals. They form when warm air picks up water vapour from the land or sea and carries it into the sky turning it into water droplets or ice crystals!

The study of clouds is called Nephology.

Let’s learn more!

There are lots of ways to describe clouds but they are usually named based on their height in the sky, their shape or the weather they can bring!


  • If a cloud name starts with “cirr-” then you know it must form very high in the sky (over 20,000 feet).
  • If a cloud name has “Alto”- in it then it is in the middle section of the sky (between 6,500 and 20,000 feet).
  • Clouds with “Strato-” in the name are found in the lowest part of the sky (below 6,500 feet).
The clouds that are really high in the sky are mainly made up of ice crystals as the air is so cold.
Clouds at ground level are called “fog”.


Did you know…all clouds are white but can appear grey or dark when seen from below? This may be due to the amount of water they contain and shadowing by clouds above them.

Clouds named according to their shape will contain one of these Latin words in their name…
  • Cumulus” – heap
  • Stratus” – layer
  • Cirrus” – curl of hair
Cumulus Clouds
photo credit: Nicolai Grut via photopin cc
Cirrus Clouds
photo credit: Gerry Dincher via photopin cc


Alrostratus Clouds
photo credit: Anita363 via photopin cc

Therefore a cloud named Altostratus would mean a cloud that forms in layers and sits between 6,500 and 20,000 feet above land.

Did you know... other planets contain clouds made up of chemicals other than water? Venus has clouds made up of sulphuric acid, chlorine and flouride. Neptune is covered by bright blue methane clouds!

The latin word “Nimbus” is used to name rain clouds!

Cumulonimbus Clouds
photo credit: izoo3y via photopin cc

Clouds called Cumulonimbus are often referred to as thunder clouds as they usually bring thunder storms!

Cumulonimbus clouds are the tallest of all the clouds.
Cumulonimbus looks a bit like a giant cauliflower in the sky!
Did you know… a sinlge cloud can hold billions of pounds of water?

Clouds are carried along by the wind and can often travel quite fast;

Thunder clouds (Cumulonimbus) usually travel about 64 kilometres per hour (kph). The highest clouds (above 20,000 feet) can reach speeds of  over 160 kph!

An experiment to try at home:


Make a cloud in a bottle!


You will need… an empty 2 Litre plastic bottle, warm water and a match.


What to do… Fill the plastic bottle one third full with warm water.  Put the cap back on and squeeze and then release the bottle.  Nothing happens. Ask an adult to light the match and put it into the bottle.  Replace the cap quickly.  Try squeezing and releasing the bottle again.  What happens this time?


So what is happening? Once the match has been added to the bottle a cloud forms when you squeeze and then release the bottle (if you squeeze again the cloud dissapears and reappears when you release).  To make a cloud you need water vapour, small particles (like the smoke) and a decrease in air pressure.