A few weeks ago we got a winter surprise in Houston. The temperatures dipped below freezing for several days and it snowed/sleeted! Today it’s sunny and in the 70s so that seems like a distant memory. But it’s still winter for most of the country so hopefully you can try this experiment somewhere where the temperatures are colder.

My kids were so excited to see frost outside (and then eventually sleet) during the below freezing temps because it’s very rare where we live. My daughter told me she wanted to bring a cup of water outside to see if it would freeze overnight. I was so excited that she initiated a science experiment on her own!

Water changes phase and freezes to ice at 32o F and below. We had perfect conditions to turn water into ice that day when the temperatures remained in the 20s all day. Also, water has less volume than ice, so we could also observe the volume expanding in our cup. 

This is a very minimal effort for very big reward STEM Snow Day activity. Your kids will love this and remember it for years. My daughter was really proud to think of this idea, and I had a proud mom moment knowing that all our science experiments are sinking in. I did this activity with them in the past when it was below freezing outside, and I’m glad she’s remembered it (whether consciously or subconsciously).

I shared this experiment in an Instagram reel and it went viral (for me!) with almost 20k views so far. Check it out below, then keep reading for the full, super simple instructions.


If doing this experiment outside during freezing temperatures as we suggest, please be mindful of your surroundings and weather conditions. Wear appropriate winter clothing for the temperatures, watch your step and beware of ice (we had ice on our back patio and nearly slipped and had a bad fall on it).


  • Cup
  • Water
  • Below freezing temperatures (32oF/0oC or below)


  1. Fill a cup with water
  2. Bring the cup outside and find a flat, open spot to place it (preferably away from house or other objects that may give off heat)
  1. Check on the cup periodically (I suggest every half hour or so) to see how long it takes to freeze the water!
Still water when we set the cup outside
After 4 hours the water was completely frozen
At 10am the following day my daughter was happy to see the water was still frozen (our temps were still below freezing)

Our water was frozen when we checked on it after 4 hours, but I wish we checked sooner because I think it had been frozen for awhile. That’s why I suggested checking on it every half hour so you can observe the freezing process.

STEAM Concepts Learned:

Water freezes to ice at 32oF or 0oC. The water is changing state from a liquid to a solid. As water gets colder, the molecules slow down, eventually becoming still in a hexagonal pattern. In this pattern the water molecules are further apart than as a liquid, so that is why ice takes up more space in its container than water. We noticed how the ice expanded in our cup.

How quickly your water freezes will vary greatly depend on the temperature of the water, the temperature outside, the volume of water, and the size of container (wide with greater surface area exposed to air vs narrow with smaller surface area exposed to air). These factors can all be varied to change the experiment and results (and would make for a great science fair experiment!).

My daughter was overjoyed when she came outside to find the water frozen! Her enthusiasm for this experiment made my Mama heart so happy!

Let us know if you try this simple activity on a cold day. My kids love doing this every time we have a rare freeze here in Houston. I can think of lots of ways for my daughter to expand on it for future science fair projects because it’s a topic that interests her. I think any STEAM activity (no matter how simple) is worthwhile if it gets your kids excited about science!


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