Introduction to Winter Weather
There is a huge difference between cold rain and freezing rain. The diagrams to the right show you the differences in precipitation types based on changes in temperature with height. Cold rain starts out as snow and for most of the way down is snow and is frozen. Right before it hits the from there is a large layer of warm air that heats the snow so it melts. The snow melts to rain and nothing is frozen when it hits the ground. Freezing rain is different. Freezing rain starts at snow then melts in a big deep warm layer. The snow completely melts in the deep warm layer before entering the small cold layer again. When the now rain hits the cold layer it get colder and only when the rain hit an object it then freezes.
Sleet is very different. It is a ball of ice. Sleet starts as snow and then melts. At high elevation it is cold or below 32 degrees Fahrenheit. Anything above that snow will melt period. Sleet starts as snow and falls through a cold layer so it will stay in the form of snow. Then the snow gradually melts in the shallow warm layer. The layer is shallow so the snow will not be able to fully melt. Once the partially melted rain get through the warm layer it hits a fairly big cold layer again. At this point the ice (melted snow) has entered into the final layer the ice is able to turn itself into sleet. The diagram for this is to the right. You can clearly see the cold and warm layers that the snow, ice, and sleet entered.
Snow is frozen. It is always below 32 degrees Fahrenheit. Once snow beings to fall it stays in a deep cold layer and doesn't come in contact with anything above 32 degrees Fahrenheit. It starts at snow and stays that way all the way until it hits the surface. Depending on the surface that it hits will determine whether it will melt or stay in its snow form. A lot of types of precipitation start as snow because it starts to fall high up, and it is cold in an high or increasing elevation. There is a diagram below of snow traveling to the surface.
A jet stream is a narrow band of strong winds in the upper atmosphere. In winter, it separates warm air form cold air. You can see the jet stream, a red band, in the diagram to the left.
Cold air damming or CAD occurs when a shallow layer of cold air becomes trapped at the surface, with warmer air just above it. What does cold air damming bring? It really depends on how deep the cold layer of air is. When cold air damming works together with a storm system that transports moisture into area, wintery participation occurs. The graphic to the right shows cold air damming over North Carolina.