Weatherz School: Anthropogenic snow

When you hear “man-made snow,” you might imagine a snow gun at a ski hill making fresh powder. While it isn’t quite the same as firing up a snow machine, when the conditions are right, snow that falls from the sky can be traced back to man-made sources. The term for this is anthropogenic snow.

There are a number of spots in the Northland that can be sources of anthropogenic snow, particularly along the Iron Range. Most of these are industrial plumes, but, bringing it back to ski hill machines, even those can seed snow formation.

What happens is the steam produced from smoke stacks adds moisture and warmth to the clouds. This gives the natural snow-making process a boost as particulates act as ice nuclei for snowflakes to grow on. Clouds and snow are spread downwind of the industrial plume.

This is fairly common, usually only producing flurries or a light dusting. In rare cases, it can be more impactful.

In November, 2020, a plume of snow in Hibbing brought visibility at the airport down to less than a mile for a time. On New Year’s Day 2021, Spirit Mountain snow machines ended up seeding snow bands that brought 1-2” to parts of Duluth.

The most extreme case of anthropogenic snow that I found wasn’t in the Northland. In February 2014, narrow snow bands formed from power plants near Amarillo, Texas and lead to extremely localized accumulation up to 5 inches! How did that happen?

A number of factors fell into place. First, the air near the surface was already cold and saturated with freezing fog. Next, the temperatures were in the perfect range for ice crystal growth.

Lastly, there was a warm air inversion with temperature rising with height. This kept the warmth and moisture from the power plant trapped near the surface, so the snow-making process was extremely efficient.

As far as anthropogenic snow events go, the Amarillo incident was certainly an extreme case. But knowing it can happen gives “man-made snow” a new meaning.