Hobbies And Interests
Making Snow
Snow is formed in a special kind of cloud, called a cold cloud. These clouds form above the freezing line of the atmosphere. Snowflakes are created according to the ice-crystal model, also known as the Bergeron process. The water vapor in the cloud, called super-cooled water, remains in the liquid state despite the below freezing temperatures. Tiny particles in the cloud, such as dust, provide a nucleus around which the super-cooled droplets can coalesce and freeze. As more droplets freeze to each, they grow into snowflakes. When they are too heavy to be supported by the upward flow of air, they fall to the ground as snow.
Low-Pressure Systems
Air always flows from areas of high pressure to areas of low pressure, seeking equilibrium. Low-pressure systems are critical to the formation of snow. Cold air is found to the north of the low, while warm air is found to the south. Low-pressure systems have a counter-clockwise circulation. This pushes the cold air to the south along the western side of the low, while pushing the warm air to the north along the eastern side of the low. The leading edge of the cold air is called a cold front, while the leading edge of the warm air is called a warm front. During the winter season, it is the warm front that triggers snowfall.
Warm Fronts and Clouds
Warm fronts represent a boundary between warm air and cold air, where the warm air is advancing. Because the warm air is less dense, it rises up and over the colder air. This creates a gentle slope of warm air in advance of the warm front. As the warm moist air slowly rises, its water vapor begins to condense, forming an expansive layer of clouds called stratus clouds. When these clouds begin to produce light to moderate precipitation, they are called nimbostratus clouds. When temperatures are cold enough, it is these nimbostratus clouds that produce snowfall.
Snow or Sleet
When snowflakes begin to fall from the nimbostratus clouds, the temperatures they encounter on the way to the ground determine whether they remain snowflakes, or become sleet. If temperatures remain below freezing, the snow reaches the ground. These conditions occur well in advance of the warm front, where the nimbostratus clouds lie above the layer of cold air that is in place to the north of the low-pressure system. The closer to the front you get, the warmer the temperatures at the surface become, eventually causing the snow to turn into sleet. However, if the relatively warm air behind the warm front is below freezing, snow will fall even along and behind the front.