How to build the ultimate snowman, according to science

Anyone who has tried to have a snowball fight, or build a snowman only to have the snow fall apart in their hands, will know that some snow is better. That’s because the properties of snow vary greatly depending on temperature and moisture.

The best snow for building snowmen is moist or wet snow, which forms when the air temperature is just above freezing — between 0°C and 2°C — meaning that some of the snow melts, creating free water between the ice crystals that acts like glue. Ideally, the snow should be around 3 to 8 per cent moisture. Any more than 15 per cent moisture, and snow becomes slush and too wet to hold a shape.

Freshly fallen moist or wet snow forms as dendrites – the classic branched snowflake shape – and the branches provide more surface area for the water ‘glue’ to stick to, making this type of snow ideal for snowballs and snowmen. When temperatures drop well below freezing, there is little or no liquid water to act as glue, and the ice crystals instead tend to form as flat plates, which have a lower surface area, making them less sticky.

There are other things to consider when building a snowman. You’ll want a level area of ground; ideally not a driveway because tarmac tends to absorb heat, which can melt your snowman prematurely. Similarly, building your snowman in a shady spot will help it last longer.

Start by packing a ball of snow in your hands. The warmth and pressure from your hands will slightly melt the snow, creating more watery glue to hold the crystals together, which will refreeze once you’ve finished building, making the snowman stronger. Roll each ball across the snow, aiming for a roughly 3:2:1 size ratio for the base, torso and head to maximise the snowman’s stability. Slightly flatten the top of the ball before you stack the next one on top, and reinforce the base of the snowman by packing extra snow around the bottom.

Read more:

• What is watermelon snow?
• Why snow days are still vital in a post-COVID world
• Is Christmas food and drink putting our health at risk?

Asked by: Glyn Ellis, Cardiff

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