One of the hardest things to explain is how different types of precipitation form and fall during the winter.

What You Need:

· 3 ice cubes

· Paper towel or paper plate

· Freezer

What To Do:

· Watch my video demonstration in full before you start. It will really help for you to start by understanding what is going to happen and in what order all of this needs to happen.

· Start with 3 ice cubes

Pro tip: the smaller the ice cubes the better because they will melt faster
Pro tip: put a couple drops of food coloring into each ice cube – a different color for each to help tell them apart

· Start with all three ice cubes in the freezer. Take out the first ice cube – this will show us how rain falls during a winter weather event. Set that on your plate or towel and leave it.

· Take out the second cube – this will be sleet. Let is sit on the counter until it *partially* melts. After noting that is has melted a bit, put it back in the freezer so it can refreeze.

· Take out the third cute – this will be snow. Hold onto it while you talk about snow, but never set it down and leave it. When you’re done talking about snow, but this ice cube back into the freezer.

What is Happening:

First, we are only talking about types of precipitation that are possible in winter. What we talk about today does not show us how summer thunderstorms develop. Even though it is also frozen, hail does not form this way. You can click here to learn how hail forms!

Second, snow grows in a very specific region of the atmosphere. If the air there is not cold enough or saturated enough, you can’t grow snowflakes. In that case you can only see rain or drizzle. Snow and sleet would be impossible if snowflakes don’t grow in that region. So for today’s activity, we are assuming the “snow growth zone” is cold enough and saturated enough to grow snowflakes. Now we will watch what happens to those snowflakes as they fall from the cloud down to us here on the ground. You can reference this image from the National Weather Service to help understand the different atmospheric profiles through which a snowflake falls before it gets to us.

Rain

After the snowflake forms and falls out of the cloud, at some point it falls through a large layer of warm air in the atmosphere that extends down to the surface. That warm air completely melts the snowflake, so we see it as rain.

Freezing Rain/Drizzle

Freezing rain falls the same way as regular rain, but the surface temperature is below freezing. When the rain falls and makes contact with an object (your car, back deck, the road, etc.) it freezes because the rain is supercooled, and the object is colder than freezing. Drizzle can also freeze on contact.

Sleet

After the snowflake forms and falls out of the cloud, it falls through a shallow layer of warm air at some point in the atmosphere and partially melts. Then it falls through another layer of air that is colder than freezing, so that partially melted snowflake refreezes into a small ice pellet.

Graupel

Graupel is also a form of small ice pellets that fall from the sky, but they form a little differently. Bits of water and ice freeze on a spec of dirt or dust or some other pollutant. The atmosphere must also be cold enough all the way down for this to make it to the ground without melting.

Snow

After all of this, snow is pretty basic! Snow forms in the cloud, falls through the atmosphere with temperatures at or below freezing all the way to the ground, and stays intact as a snowflake until it gets to us here on the ground.

How Different Types of Winter Weather Form