What are air masses?

Air masses are big groups of air that have the same temperature and humidity all through them.

Imagine you're playing outside on a sunny day, the air feels warm and dry. Now imagine you run into a cloud, and suddenly it starts to rain, the air now feels cool and wet. That’s like when one air mass meets another air mass, and they change what the weather is doing.

Air masses form over places like oceans or continents. If a big group of air sits over a hot desert for a while, it gets warm and dry, just like how your skin feels when you sit in the sun for too long.

But if that same air moves over a cold lake, it can get cool and wet, like when you step out of a pool on a chilly day.

Air masses don’t stay still. They travel across the Earth, bringing their temperature and humidity with them. That’s why one day it might be sunny and warm, and the next day it's cloudy and rainy, because a new air mass has arrived!