Why is it that in Very Hot days, Cumulonibus clouds form near the mountains?

Question

you're not mean meangirl :) thanks!

Answer 1

I think the answers so far are pretty good, but I'd add that mountains cause cumulonimbus clouds to form another way besides "pushing the air up" or orographic lift. Many thunderstorms form when air in contact with the ground is heated and rises as bubbles (thermals). If the air has to be lifted a long way to reach the level where clouds form, it may not have enough buoyancy. Also, there could be a cap such as a temperature inversion that prevents the warm bubbles of air from rising any farther. These factors are often in place here in Southern California when we get our summer thunderstorms. However, the mountains are above the inversion layer and the air doesn't have to be lifted too far, so it is much easier for cumulonimbus clouds to form there than over the coastal sections.

Answer 2

Meangirl is correct. The technical term for why this type of Cumulonimbus cloud forms is "Orographic Lift." In lamens terms, when the winds blow against the mountains, the air is forced upwards. As air rises, it cools and condenses into clouds...and since the winds that blow against mountain chains are fairly stout, the clouds form rapidly and vicously to produce typically violent thunderstorms. Finally, the temperature doesn't always have to be "very hot," but the hotter the better.

Answer 3

Three ingredients are needed for the formation of a perfect cumulonimbus cloud:
Plenty of moisture.
A mass of warm unstable air.
A source of energy to lift the warm, moist air mass rapidly upward.
Typically, the clouds form around front lines, near oceans where sea breezes provide storm energy, or over mountains which push the air upwards.