Snow Can Happen For Lots Of Surprising Reason

Radar image from Chicago in late November. The purple plime
heading southeast from the southern tip of Lake Michigan is light
snow created by a steel plant in Gary, Indiana. .The loop of snow
further north was created by planes getting ready to land at
O'Hare. Image from Matthew Cappucci/Washington Post 

There's a lot of reasons why it snows in the winter.

Usually, it's just a matter of a storm system creating enough lift in the atmosphere for air to rise, and moisture to condense out as snowfall when temperatures are below freezing.

Sometimes moisture coming off a relatively warm lake or ocean during cold weather can condense when it hits the cold air, causing sometimes epic snowfalls near the shore.

And sometimes, us humans can cause snowfalls, although the manmade snowfalls are usually pretty minimal.  There have been some noteworthy examples of this in recent weeks.

In Nebraska, some industrial plants around the city of Norfolk belched steam into some chilly air. The warm steam condensed in the cold air and it snowed for many miles downwind from the plants. There was one report of at least two inches of new snow 30 miles downwind of the Norfolk plants west of Omaha.

This "storm" actually prompted the National Weather Service in Omaha to issue a winter weather advisory for the affected area. The wind eventually shifted, and some snow and freezing drizzle caused by the smokestakes in Norfolk fell on Omaha.

Another industrial plant last week created a plume of snowfall in the Minneapolis-St. Paul, Minnesota area.

In late November, a large steel plant in Gary, Indiana belched steam, which turned into a narrow stripe of snowfall heading southeastward up to 18 miles from Gary.

That same day, airliners circling near O'Hare Airport north of Chicago helped produce loops of snowf flurries over Lake Michigan, just offshore of Chicago, says Capital Weather Gang.

Usually, to get these man-made snowfalls, it has to be cold - Duh! But the air has to be pretty wet as well. In all the cases above, the air was not particularly dry.

Snow created by industry is by no means a new phenomenon. It has happened for decades. Nowadays, radar has gotten much better at detecting precipitation, so "smokestack snow" has become more noticeable.

I work very close to a large wood-fired electricity generating plant in Burlington, Vermont. I have occassionally seen a bit of snow fall from the billowing steam clouds this plant produces.

A thunderstorm over Atlanta, Georgia. Sometimes, cities can manufacture
their own thunderstorms. Photo b Eyebeam Photography/Getty Images

Snow is not the only way we humans can affect local weather. Studies have shown that some cities can create thunderstorms. Atlanta is a noteworthy example. Is often hot and humid there in the summer, which is a great ingredient to produce storms.

Cities tend to be hotter than the surrounding countryside. Hot air rises. Rising air can create thunderstorms.  Atlanta and other big cities also have skyscrapers. Wind hitting the skyscrapers is forced upward. That little nudge upward can be just enough to initiate thunderstorms.

The result is that Atlanta and many other cities have a somewhat greater number of thunderstorms each year than the surrounding countryside.

All this is an indication that yes, as we talk about climate change, humans can affect world-wide climate. But on a more benign level, we can easily change local weather