very rare weather phenomenon

A snow roller is a rare meteorological phenomenon in which large snowballs are formed naturally as chunks of snow are blown along the ground by wind, picking up material along the way, in much the same way that the large snowballs used in snowmen are made.

Unlike snowballs made by people, snow rollers are typically cylindrical in shape, and are often hollow since the inner layers, which are the first layers to form, are weak and thin compared to the outer layers and can easily be blown away. Snow rollers can grow as large as a foot in diameter.
The following conditions are needed for snow rollers to form:

• The ground must be covered by a layer of ice that snow will not stick to.
• The layer of ice must be covered by wet, loose snow with a temperature near the melting point of ice.
• The wind must be strong enough to move the snow rollers, but not strong enough to blow them too fast.
• The ground must have a slope, at least where the snow rollers start rolling.

Because of this last condition, snow rollers are more common in hilly areas. However, the precise nature of the conditions required makes them a very rare phenomenon.  This information came from the National Oceanic and Atmospheric Administration (NOAA). 


Snow rollers might be rare, but we had 'em at our place.  Brent headed to his office Friday morning after a couple of inches of snow whitened the ground on Thursday night.  He called me and told me I had to come see "hundreds of snowballs" at his office.  I loaded up the kids, grabbed the camera and headed out the door so Lucas could see them before he went to preschool. 

I wish I would have used something to gauge the size of the snow rollers for the photo... The one above, in the lower right, was easily 12"in diameter.  You can see their unique, cylindrical shape.  

In the twenty or so minutes we looked at them and took pictures, I saw several roll away.  They looked so light.  Brent inspected one and said it was hollow, just as the NOAA information indicated.  

These pictures were taken at 8:30AM.  By 4:30PM, two thirds of the snow rollers had rolled away.