Every winter, we are often asked why, when it is so cold outside, it isn't snowing? Instead, we'll get a cold rain or maybe some sleet.
There are four main types of precipitation that we see here in East Tennessee: snow, sleet, freezing rain and rain.
They all begin as snowflakes when they fall from the sky, but the depth of cold or warm air within the atmosphere determines what type reaches the ground.
Snow begins as a snowflake and reaches the ground as a snowflake when the atmosphere is below freezing from top to bottom.
Sleet begins as a snowflake but partially melts when it encounters a pocket of above-freezing air. It then refreezes before reaching the ground as an ice pellet. Sleet will bounce.
Freezing rain begins as a snowflake but melts to a raindrop when it encounters a pocket of above-freezing air. This layer of warm air is thick enough to keep the raindrop in the liquid form all the way to the surface. The ground is at or below freezing and the drop refreezes on impact with the cold ground. This is the most dangerous type of winter precipitation.
Rain begins as a snowflake but encounters warm air all the way to the ground and reaches the surface as liquid.
**As we begin to see a threat from any type of winter precipitation, winter weather watches and warnings will be issued for the area**
This story is part of our Winter Weather Week of coverage. You can see Chief Meteorologist Todd Howell’s Winter Weather Forecast on Wednesday at 6pm.
(© 2016 WBIR)