What happens when air masses bump into each other?

Question

What happens when air masses bump into each other?

Answer 1

When air masses of different temperatures collide, it causes lightning, thunder and rain.  The greater the temperature difference difference, the more severe the reaction.

Answer 2

Usually air masses do not actually collide, one from behind overtakes the air mass in front of it.  A colder and denser air mass will displace warmer moister air, pushing it up.  This forms a typical thunderstorm cell.  As the warm air moves up it also starts to cool.  Eventually it will cool enough to force the humidity out- rain.  (Keep in mind the warmer the air the higher the water content it can hold.)

When warm air overtakes a cold air mass it will climb it  and in a more gentle manner release its humidity, with wide spread clouding and gentle rains- often very persistent.

Sometimes air masses to collide, usually vertically.  A cold dense mass of air will suddenly fall through a warmer air mass.  This provokes very sudden strong storms.  Pilots refer to them as micro bursts. They can be surprisingly violent and short lived.

Tornadoes are a special case of large scale bursts with hot air rising, suddenly cooling and flowing back down displacing the air below.  The total energy release of all this is lightening and very high winds over hundreds of yards.  Usually a storm large enough to provoke a tornado will be large enough to have several tornado cells spread out over a front of a few miles.  It is not well understood why some spots do develop into tornadoes and other spots that seem to have all the requirements do not.