What would you expect to cause a drop in air pressure?

Weather patterns are a common cause in barometric pressure drops. When low-pressure weather systems move in over a certain area, not only is pressure in the atmosphere shifted, but it causes the barometric pressure reading to drop. A low-pressure system indicates that low-pressure air rises and begins to cool.

Explanation:

Cool temperatures cause air pressure to drop. When gas molecules cool, they move more slowly. Decreased velocity results in fewer collisions between molecules and air pressure decreases.

Explanation:

answer; necessity-driven;