John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Credit the “Wegener-Bergeron process” for making this rare blotch of human-induced snow.
Drop a 10-ton bag of flour from space onto the western Netherlands, and you’d get the scene that appeared in mid-January: an oblong patch of snow on an otherwise barren section of agricultural land. Was it an extremely local attempt at cloud seeding? Some fun-loving Dutch who’d frozen snow the winter prior, and decided to have a massive snowball fight?
The explanation did likely have a human, though unintentional, origin. The scene captured by a U.S. Geological Survey satellite on January 19 in Heensche Molen was probably the result of a rare weather phenomenon involving freezing temperatures and industrial activity—specifically, the “Wegener-Bergeron process,” according to NASA. The space agency talked with a local meteorologist, Wim van den Berg, who explained how that process works. Here’s the gist:
Fog-induced snow (not a formal scientific term) typically forms next to industrial sites. Big chimneys release water vapor and other gases and particulates, which can lead to the formation of fog. It also turns out that these emissions can create snow when the weather gets cold enough. ...
That is likely what happened in January 2017, van den Berg believes. “After many days with fog and/or low clouds and subfreezing temperatures, on January 17 several places reported snow,” he wrote in an email. “It was very local, mostly west of industry,” as surface wind was light easterly, “but it did cause some unexpected slipperiness.”
Industrial snowfall is not a European anomaly. Last winter, steam from energy plants likely contributed to snow showers in St. Paul and Minneapolis. And in 2014, a dusting of snow in the Chicago area was attributed to soot discharged from smokestacks. The National Weather Service tweeted at the time: “Very isol'd snow accums this AM likely related to particles from smokestack plumes aiding in snow crystal formation.”