Here's why:

* Pressure and Density: Air pressure is the force exerted by the weight of air molecules on a given area. Higher density air means more molecules packed into a given space, leading to higher pressure.

* Low Pressure = Fewer Molecules: A low-pressure area has fewer air molecules in a given volume, meaning less pressure.

* Weather Significance: Low-pressure areas are often associated with stormy weather because air flows towards them, seeking to equalize pressure. This rising air can lead to cloud formation and precipitation.