colliding air masses

a fast-moving warm air mass overtakes a slower cold air mass; the warm air moves over the cold air

sinking air where clouds cannot form

cool, humid air masses form over the icy cold North Atlantic Ocean

hot, dry air masses form mostly in summer over dry areas of the southwest and northern Mexico

A huge body of air in the lower atmosphere that has similar temperature, humidity, and air pressure at any given height

warm, humid air masses form over the Pacific Ocean

when a faster cold air mass runs into a slower warm air mass; the denser cold air slides under the lighter warm air; warm air pushed up

rising air, which allows clouds to form

large air masses form over Canada and Alaska and can bring bitterly cold weather with low humidity

when cold and warm air masses meet but neither one can move the other