Why Can I See My Breath on a Cold Day?
On a cold day you can see a small steamy cloud each time you blow out your breath. Your breath has moisture in it. Air is warmed and moistened as it is drawn into the body by the nose. When you breathe out that moist, warm air into the cold out-of-doors air, your breath suddenly cools.
Some of the moisture in your breath changes into tiny water droplets, which form a small steamy cloud. Of course, there is just as much water in your breath on a warm day, but then it remains in the form of an invisible water gas as it comes from your body.
This scientific process is called condensation. When you exhale when it’s cold outside, the water vapor in your breath condenses into lots of tiny droplets of liquid water and ice (solid water) that you can see in the air as a cloud, similar to fog.
When it’s warm out, though, the invisible water vapor gas stays invisible, because the warm air provides energy that allows the water vapor to remain a gas. As temperatures drop, it’s more likely that you’ll be able to see your breath.
There’s no exact temperature at which condensation will occur. Many environmental factors other than temperature can play a role in condensation, including relative humidity (the amount of moisture in the air). When it falls below 45° F, though, you can usually expect to be able to see your breath.