Weather Academy: Make a Front in a Glass

Published: Sep. 27, 2021 at 6:26 AM CDT
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MONROE, La. (KNOE) - Last week on the Weather Academy, we explained how cold fronts work. And today, we are going to be conducting an experiment that you can easily do at home to help you get a better understanding of fronts.

What you’ll need:

  • Food coloring
  • Two identical glasses
  • Hot water
  • Cold water
  • Spoon
  • Something to be a divider, we are using a piece of cardboard in a ziplock bag.
  • Large tin or dish (optional)


  1. Have the cold water and hot water in two separate glasses. Make sure the glasses are as full as possible. The warmer/colder the water is, the better this experiment will work.
  2. Place both glasses into the large tin or dish. This will act as our splash pad and catch any water that might spill out in the later steps of this experiment. This step is optional but is recommended if you are trying to avoid a mess.
  3. Add red food coloring to the hot water and blue food coloring to the cold water, then use the spoon to make sure it is nice and mixed up.
  4. Next, we take our plastic divider and place it on top of the blue water. Push it firmly over the top of the glass to create a bit of suction.
  5. This is the difficult step. We are going to flip our blue glass on top of the red glass. You want to have it, so the divider is preventing the water from mixing. Try to line up the glasses as much as possible.
  6. Carefully pull out the divider and watch what happens!
  7. Repeat the steps above but this time, flip the red glass on top of the blue glass.

This experiment shows the power of density.

The first time we did this experiment, the red and the blue mixed together, creating that deep Indigo color. The second time we put the red on top and the blue on the bottom, you can notice that they’re still very distinctly red and blue. There is some mixing in the middle where we have a little bit of that Indigo. For the most part, the colors are pretty separated. The reason for this is because our cold water is denser than our warm water. That means our cold water wants to sink. So when our cold water was on top, it wanted to sink through the warm water to get the bottom of the glass, and that’s why we had all of the mixing. In the second run of the experiment, the cold water was already on the bottom, so while there is some mixing in the middle, for the most part, you notice that we still have our red on top and blue on the bottom, which indicates that the cold water did not rise. When a cold front moves through the region, the cold air is much denser than the warm air. This forces the warm-up and over the cold air. This causes clouds to form, and that’s why we usually see showers and thunderstorms when a cold front approaches. When a warm front moves through the region, there isn’t as much mixing in the atmosphere, which means we won’t see as many thunderstorms as we do with a cold front. We will likely still see clouds and rain, just not the thunder and lightning.

Thank you for watching this week’s Weather Academy episode. If you try this out at home, please send us your photos and videos! We’d love to feature you in next week’s weather academy segment.

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