Why do the Rocky Mountains get so much snow?

Question

Yes, I KNOW it's cold there. Don't tell me that. I'm looking for a scientific answer.

If cold air sinks...why is it cold up high? I know that warm air holds more moisture... So that might explain the snow.

This is for a science homework thing. Please help!

Answer 1

Let's say a mass of air travels across Nevada and Utah and arrives in Colorado. This is what generally happens anyway because of the prevailing westerlies, as you know.

This mass of air has moisture evaporated in it, basically from water that evaporated from the Pacific Ocean. (In simplistic terms...) the air may have a temperature of 55 degrees, and a dewpoint of 45 degrees. i.e., if it were to be cooled to 45 degrees, the relative humidity would become 100%, and it could not hold any more water molecules.

It is forced to rise as the prevailing westerlies force it up and over the Rockies.

I'll ignore the question about why it is cooler at higher altitudes/elevations, because answering that would make my answer way too long, but suffice to say that the (dry adiabatic) lapse rate is 9.8 degrees celsius per 1km, or roughly 6 degrees per 1000 feet. A mass of 55 degree air that crosses the western USA at around 4000 feet elevation, then gets pushed up to 12,000 feet of the Continental Divide expands and cools by about 48 degrees. (8000 feet times 6 degrees per 1000 feet) Again, I'll warn that this is tremendously simplified. As it crosses the Divide, it is cooled to about 7 degrees F.

Now, since that air has a dewpoint of 45, what must happen? Condensation. The cooling condenses out the moisture in the form of snow (and also rain at lower elevations), and the air is "dried out" to a new dewpoint of that same 7 degrees.

The air travels on down to Denver and points eastward (This is also why it is relatively dry on the High Plains, and few trees are seen there, but rather it is an ocean of prairie grasses, which can survive with less rain than trees need.), but the snow remains on top of the mountains!

You might also try searching "orographic lifting" if you want to learn more.

Answer 2

They're close to the ocean. The air is filled with humidity. Cold air can't hold as much water vapor than hot air.

The hot air down in Vancouver gets filled with humidity because of the ocean. The wind pushes the air awy from the ocean, towards the mountains, and once there it hits a wall, it has to go up, it gets colder and the extra humidity falls as snow.

Answer 3

Its blocking 3 countries from cold air and snow. When the snow come west to those three countries,the mountains block the cold air and snow and the cold air turns into snow.cuz of cold weather and when it snows,the snow becomes hard ice and stays there.