How’s the weather? The answer depends on what kind of air mass is passing over your region.
Masses of air that have similar moisture content, similar temperature, and other characteristics in common tend to travel around the globe in big chunks that cover thousands of square miles.
Air masses get their particular characteristics from the Earth surface over which they form. Warm, wet areas like the Gulf of Mexico produce warm, humid air masses. Cold, dry areas like northern Canada produce cold, dry air masses. Air masses are called high pressure systems or highs 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, because air masses are always on the move, bumping into each other as they travel around the globe.
