What is windchill? Windchill is the effect of wind adding to the problem of cold.

When a wind blows over a wet surface, it tends to cause the evaporation of moisture from the surface. To do this it takes heat from the surface (it needs heat to change liquid water to water vapour).

On a warm day you may be grateful for this effect, because you would then call it a cooling breeze. But it is not the breeze that is doing most of the cooling - it is the evaporation of moisture from your skin.

But when it is very cold the same happens, and this can cause the skin to cool down so much that the body cannot put heat back fast enough. You notice it through shivering and goosebumps. When wind and moisture loss may make life uncomfortable for us we call it windchill.