We know that liquid water freezes into ice over a long amount of time. We're about to make instant ice. This is done by chilling water in a freezer and not letting it freeze into a solid.
Let's go over this simple experiment.
First, put a few unopened water bottles in the freezer. We need the water to get very cold, but not frozen. The temperature inside the freezer is below 32 degrees Fahrenheit; but, you'll notice the water can still be a liquid below that temperature.
At the two hour mark, the water was cold, but not cold enough. The bottles are ready once it looks like ice might start forming. This happened at around three hours in the freezer. Once it's ready carefully take a water bottle out trying not to disturb it. The next step is to put ice cubes in a bowl or container.
When you pour the liquid water directly onto the ice cubes, it freezes and piles up. This happens instantly.
Why does this happen? Well, because of science of course! The water in the freezer became super-cooled.
In order for water to freeze into ice, there needs to be something called a nucleation site. This is a small spot in normal water where the first ice crystals begin to form.
This water was different. It had no contaminants like dust or dirt. This allows the water to get "super-cooled". That means the water temperature was below freezing, but there was no spot for ice to form. The ice cube acted as that nucleation site for the first drop of water we poured. After that, it was a chain reaction, and a slushy, icy mix grew taller and taller.
How does this relate to our weather? Well, sometimes we have super-cooled water droplets in clouds. Don't worry though, it doesn't turn into slush like we just showed here.