Over one million people attended an open air mass in the park at the time.

A moving front is named according to the advancing air mass.

Air masses can be modified in a variety of ways.

This could be partly due to two air masses coming together.

It was here, apparently, that he hit his first unstable air mass.

What if you had huge air masses to work with?

"There's no human being responsible for this tropical air mass that passed over Chicago."

A polar air mass brought cold weather to the region yesterday.

They are an important barrier to the movements of air masses.

Tomorrow night, another cold air mass is expected, keeping the temperature in the mid-20's on Wednesday.