The word airmass is a singular noun. The plural is airmasses.
Air does not remain in a given place. A country does not have an 'airmass'.
it become a storm
The warmer airmass that was coming would mark a positive change in the weather.
An airmass that is very warm and dry would be very light and have a tendency to rise up.
Compared to a maritime tropical airmass, a maritime polar airmass has lower temperature and less water vapor.
It is cold and dry.
part of speech
The part of speech for this particular word is a noun.
what part of speech is beneath
what part of speech is work
adverb
Sashay is a verb. It means to walk in an exaggerated, showy manner, often with hip swaying.