Snow Rolls From 69 News Viewers

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69 News viewers from Lehigh County, Northampton County, Berks County, and Schuylkill County sent pictures of snow rolls on their cars.

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North Catasauqua, Northampton County.  Credit: Russell Reinhard.

For this to happen, the snow needs a certain texture: wet and dense.

We got wet snow Friday night because temperatures were at or above freezing as the snow fell.  So, the snowflakes were close to melting into raindrops.  This is why the snowflakes were rather wet and not dry, fluffy flakes.  The more the temperature drops below freezing, the drier and fluffier snow gets.

Friday night's wet snow created a layer of thick snow.  Then, the snow switched over to rain.

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Credit: Robert Gilson

The rain helped make the layer of wet snow more dense and more stuck together, which created the ideal texture for snow rolls.

Fast forward to Saturday as the layer of wet, dense snow started to melt on windshields.

The snow at the top of the windshield was not melting as fast as the snow in contact with the rest of the windshield.  So, the snow became top heavy.  

Once it got heavy enough, the top part of the snow started to roll because of the slant of the windshield, and it kept rolling because of how dense the snow was.

While gravity led to these snow rolls, you can see similar formations in fields with a hill sometimes. 

Patty Shreve - Berks County

Credit: Patty Shreve - Berks County

For field snow rolls to happen, there has to be some wind.  Then, there has to be thin coating of fresh, wet snow.  Next, the wet snow needs to fall on top of a crusty or hard layer of snow.  If all those boxes are checked off, then the wind can lead to these rolls of fresh snow.

Patty saw one of those field snow rolls outside her door in Berks County last week.

Thanks to everyone who shared a picture!