There is a wide variety of conditions that can cause this: A pool of cold air, supercell thundestorms, bow echoes etc.
fast moving
faster moving
severe weather
The kind of air mass that causes hot,humid weather are the air masses that form over places near the equator ! (Hope you have fun)
Hot and sunny. ;)
Hot and sunny. ;)
cool weather
snow
Stormy weather often occurs along the boundary between air masses or in association with a low pressure system.
Hot,dry conditions
I am not sure how to put this scientifically, but a high pressure air mass with low humidity.
A sudden change in weather is caused by an air mass.