How’s the weather? That depends on what kind of air mass is over your region. Masses of air with similar moisture content, temperature, and other things in common tend to travel in big chunks. These masses can cover thousands of square miles.
Air masses get their particular qualities from the Earth surface over which they form. Warm, wet areas like the Gulf of Mexico make warm, humid air masses. Cold, dry areas like northern Canada make for cold, dry air masses. Air masses are called high pressure systems or highs. That’s because the air in them is under high pressure, like air in a bicycle tire. Highs usually bring stable weather. It may be bitter cold or warm and sunny, depending on the season. But it doesn’t last forever. Air masses are always on the move, bumping into each other as they travel around the globe.
