John Wheeler: Roads were unusually icy during the winter's first storm

FARGO — The number of vehicle accidents Wednesday and Thursday morning around North Dakota and western Minnesota was extraordinary for the relatively light snow. The roads became covered with a thick layer of ice by Wednesday morning because the warm weather in the weeks preceding the storm had left ground temperatures much warmer than 32 degrees. What happened then, is called a flash freeze.

As the snow arrived, the temperature quickly fell into the 20s. The snow was melting on impact with the warm ground, and the thermodynamic process of melting the snow crystals into water drew a lot of heat out of the ground. The slush layer turned to ice and then the wind and light snow all day Wednesday kept that ice polished.



The ice remained until lowering winds Thursday allowed solar radiation to melt the ice off the roads. Most storms this winter will not happen under these circumstances..