Reply To: Precipitation

Louise Hahn

While all forms of precipitation start as snow high up in the clouds, there are four primary types that eventually reach the ground: snow, sleet, freezing rain and rain.

Snow occurs when the atmosphere is “cold” all the way from the clouds to down here at the surface.

Sleet and freezing rain form because of a “warm-air sandwich” in the atmosphere above our heads. Precipitation starts as snow in the cold layer at the top, then melts to rain as it falls through the warm layer, then refreezes into sleet or freezing rain as it falls through the cold layer near the surface.

For sleet to occur, the warm air layer is rather thin. A thicker wedge of cold air beneath the warm air refreezes the partially melted snow into ice pellets.

For freezing rain to occur, the warm air layer is thicker. The snow melts into rain then refreezes just as it hits the cold ground.

Since the rain is not freezing until it reaches the surface, it still falls like regular rain and therefore looks and feels the same until it freezes on the ground.

Sleet is made up of ice pellets that bounce off objects. Even though this may sound more hazardous than freezing rain, that’s not the case.

Finally, when the air is warm enough all the way down to the surface, it’s just rain that reaches down here.

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