FARGO — Freezing rain and freezing drizzle, two terrible dangers for travelers, occur several times each winter but are often difficult to predict. Freezing rain occurs when snow falls through a layer of warm air near the ground, causing the snow to melt into rain, and the rain then freezes upon impact with frozen ground. Freezing drizzle is made up of much smaller droplets and is often not associated with a warm layer. Freezing drizzle often forms in clouds where the temperature is below freezing.

Snowflakes in a cloud grow on pieces of dust or small ice crystals, and in very specific cases, notably when cloud top temperatures are between 10 and 18 degrees and the air is very dry above the cloud layer, moisture droplets will remain liquid at high temperatures. well below zero. So instead of snow, the cloud produces small droplets of “super-cooled” water, which instantly freeze on contact with any surface.

John Wheeler is chief meteorologist for WDAY, a position he has held since May 1985. Wheeler grew up in the South, in Louisiana and Alabama, and cites his family’s move to the Midwest as being important in developing his fascination with weather and climate. Wheeler lived in Wisconsin and Iowa when he was a teenager. He attended Iowa State University and graduated with a bachelor’s degree in meteorology in 1984. Wheeler worked about a year at WOI-TV in central Iowa before moving to Fargo and WDAY.