Tuesday, January 11, 2011

Question of the Week

Today in Richmond, we are experiencing a messy and somewhat hazardous mix of snow, sleet and freezing rain. 

Do you know what atmospheric conditions cause each kind of frozen precipitation?

Answer:  Winter precipitation types generally depend on the vertical temperature profile of the atmosphere.
  • Snow falls when the temperature of the entire depth of the atmosphere from the cloud to the ground is below freezing (32 F or 0 C).
  • Sleet falls when there is a fairly shallow layer of warmer air (above freezing) between the cloud and the ground but the temperature at the ground is below freezing.  Snow falls from the cloud, then partially melts in the warmer layer and then refreezes in the colder layer near the surface, forming pellets of ice.
  • Freezing rain falls when there is a deep layer of warmer air (above freezing) but the temperature is below freezing at the ground.  Snow falls from the cloud, melts completely in the warm layer and then refreezes either just before hitting the ground or on contact with the cold surface.

No comments: