雪是怎样形成的英语作文

A snow storm is usually the result of the warm air associated with an extratropical cyclone (as in the diagram above) flowing up and over the cold air surrounding part of the cyclone. The air being lifted, combined with the abundant water vapor available in the warm air mass, causes cloud water to keep forming. This cloud water is collected by falling ice particles, which grow as the super-cooled cloud water freezes. The ice particles in the clouds grow and combine to become so large that upward flowing air (updrafts) in the clouds can no longer support them, and they fall to the ground. The more water vapor there is available to the cloud, and the stronger the updrafts that cause this water vapor to condense into cloud water or ice particles, the more likely it is that snow will form within the cloud. A cold, cloudy day with no snow indicates that there is either not enough water vapor available to the cloud, or that the rising motion creating the cloud is not enough to cause snow