One of the most interesting clouds appears in the mountains and almost looks like the mountain peak is wearing a little hat. These are called lenticular clouds.

In order for a lenticular cloud to form, you need a somewhat moist and stable airmass. In this case, a stable air mass refers to one in which the air warms slightly as you climb in altitude, preventing air from rising without help from terrain and an air mass mostly void of clouds.

These conditions are important because as the moist, stable air mass approaches a mountain, it is forced to rise. As the air cools, water condenses, forming a thin cloud that ascends the mountain.

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As this air descends the other side of the mountain, it warms back up and the water evaporates. Because of this, the cloud appears as a concave sheet that lies above the summit of a mountain. This is a lenticular cloud.

While lenticular clouds themselves are not dangerous to aircraft, they are the result of air quickly rising and descending up and down the mountain. This current of air extends higher into the atmosphere above the mountain and can be very dangerous to aircraft that get too close.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.