Weather: why it snows
Self-tutoring about weather: the tutor gives a basic explanation of why snow events happen.
The following is my understanding of how snow develops.
There are two types of weather systems: high pressure areas, and low pressure areas. High pressure areas are centres of cold air, sinking to the ground. During the winter, in a continental climate, a high pressure system’s air will likely be below freezing.
A low pressure system is the opposite: it’s warm, rising air. Even in winter, in a continental climate, a low pressure system likely contains moist air above freezing. The reason is that the low pressure system usually has arrived from a warmer place with a subtropical or tropical climate.
Therefore, in a continental climate, during winter, when a low pressure system collides with a high pressure system, warm, moist air collides with cold air. On the leading edge, the warm, moist air of the low will be frozen by the cold air from the high. This frozen atmospheric water will fall as snow.
Places that get a lot of snow have continental climates and also witness lots of collisions between low and high pressure systems. In North America, the midwestern states and southern Ontario can receive significant snow because warm, moist air from the Gulf of Mexico travels up the Mississipi Valley until it collides with local cold air from a high pressure system. There are many other examples, worldwide.
Source:
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.