What causes really large snowflakes to form?

PITTSBURGH — Did you look out of your window on Saturday and see light snow quickly turn to heavy snow that consisted of bigger snowflakes?

Believe it or not, there are many different types of snowflakes, and the bigger ones that occurred recently are called dendrites. When viewed at close range or under a microscope, these snowflakes have tree-like qualities.

Dendrites occur in the atmosphere in what we call the “dendritic growth zone.” The DGZ is a zone in the atmosphere between roughly -12 degrees Celsius to -18 degrees Celsius. If you look at the image below, you’ll see sounding data for Pittsburgh for the morning of Jan. 16. The green line is the dew point temperature and the red line is the temperature, both as you go up in the atmosphere. The numbers on the bottom are the temperatures, in degrees Celsius. I’ve highlighted the DGZ in blue.

Dendrites form best when the temperature and dew point are close together within this zone. When this happens, it means the air is close to, or at, saturation.

Another factor that aids in the development of dendrites is strong upward motion within the dendritic growth zone of the atmosphere.

In the case of Saturday, we had saturated conditions within the DGZ, along with good vertical motion and a weather disturbance moving through. This combination led to heavy snow with whiteout conditions reported in some areas.

Winter Weather Advisory issued for areas as snow showers expected to continue

Cox Media Group