A photo of Mount Everest covered in snow.
Mount Everest, at 29,032 feet (8,849 meters), is the highest mountain on Earth, towering above where most clouds float. Yet, it's always covered in snow, which might seem strange since clouds, which bring snow, are usually lower down. So, why exactly does Mount Everest still have a snowy summit?
Clouds, the Jet Stream, and Everest's Height
Clouds start to form when water in the air condenses to droplets or even to ice, but this happens at lower altitudes, where it's warm enough for the transformation. Everest's peak is so high that it often resides above this typical cloud zone, with the air being very thin and the temperature not suitable for cloud formation. This perhaps brings up the question of how the persistence of snow at such an altitude is possible. Part of it has to do with the way the Jet Stream acts. This high-altitude wind current will sometimes push existing clouds up to heights where they will veil or even clear Everest's summit. When these clouds, heavy with moisture, are thrust into the freezing cold at Everest's summit, the moisture inside them freezes directly into snow. It occurs, not day by day, but from time to time, modulated by seasonal changes in the course of the Jet Stream.
The Role of Wind in Distributing Snow
Wind is another important component for holding the snowy cap of Everest together. At such heights and altitudes, winds are not only very strong but are also important mediators that blow snow around the mountain area. Snow might get blown upwards by wind like a natural conveyor, starting at a lower elevation or even from clouds that remain below, and reach much higher altitudes to be deposited. This snow can make up much of the overall accumulation as it is picked up from anywhere on the mountain and dumped at the top where it would be too cold for any to melt off or get blown away.
Orographic Lift: Precipitation From Rising Air
A diagram illustrating orographic lift.
Another process by which snow is created on Everest, separate from clouds observed at the summit, involves orographic lift. When air masses hit the giant obstacle that is Everest, they are forced to rise. This rising air cools, and its capacity to hold moisture is reduced; as a result, it condenses and directly deposits ice or snow at the summit. This means that even when the summit of Everest has clear skies, the mountain itself can create its weather. The rising air can lead to the formation of snow directly from the moisture it carries, adding to the snow cover without any direct input from other clouds.
Why Does The Snow Not Melt?
Finally, the last piece to the puzzle is to know why the snow at the summit does not melt. Well, obviously, it gets so cold there, often as low as -22°F (-30°C), that the snow does not really go away but rather settles as a part of the landscape. However, due to sublimation, some of the snow does end up disappearing; the direct sunlight turns the snow or ice directly into gas. In other words, it is so cold that solid water (snow, ice, etc.) turns directly into gas without going through the liquid phase. Adding on, the snow itself adds on to the cold weather because a large percentage of the sun's warmth is reflected back into space through something called the albedo effect.