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How power plants, rivers and even airplanes can produce snow

A KC-135 Stratotanker aircraft assigned to the 171st Air Refueling Wing, sits on the flightline during the first snowfall of the year, Jan. 16 2021, near Pittsburgh, Pennsylvania.

ALLYSON L. MANNERS/U.S. AIR FORCE

By MATTHEW CAPPUCCI | The Washington Post | Published: February 20, 2021

When it comes to snowfall, sometimes the atmosphere gets a little help from some not-so-normal places. Odds are you've heard of ocean-effect snow before, but have you ever heard of airplane-effect snow?

As crazy is it may sound, airplanes can produce snow. So can rivers, lakes, power plants, and technically even slaughterhouses.

Here's our list of some of the weirdest things that have generated their own localized snowstorms.

Airplanes

On Nov. 27, 2018, light snow broke out near Chicago's O'Hare International Airport. It traced several odd loops and lines, falling only at the lowest levels of the atmosphere. A thick blanket of overcast hung overhead, with low-level stratus clouds and frigid temperatures in the lower 20s.

It turns out the clouds were made of supercooled water droplets, or droplets of water that remained in liquid state below 32 degrees since they had nothing to freeze upon. When aircraft landing on O'Hare's east-west runway passed through them, airplane exhaust filled with soot and hydrocarbons "seeded" the clouds. That gave the droplets something to gather around and freeze upon, nucleating a snowflake and allowing snow flurries to be spotted on radar.

Since the atmosphere was cold and moist even to ground level, some of those flurries reached the ground, resulting in an episode of true airplane-effect snow.

The same thing happened in Dallas just last week.

Power plants

When the air is cold, it can hold very little moisture. That's why our hands crack in the wintertime and our lips become chapped.

Adding moisture to the air will increase its humidity until a certain point, at which moisture overwhelms the air's ability to hold it. That's when the atmosphere becomes saturated, squeezing out any excess humidity in the form of rain or snow.

The steam released by power plants is often a significant source of moisture. When the air is warm in the summertime, it can carry and diffuse this moisture. But on the coldest of winter days, that extra moisture occasionally falls as snow.

In 2013, the Beaver Valley Nuclear Power Plant near Shippingport, Pa., produced its own swath of accumulating snow. A similar phenomenon happened in 2018 in Ohio. The same cold air outbreak also triggered a hundred mile long plume of snow downwind of the Alliant Energy Portage Power Plant in Portage, Wis., dropping up to half an inch of accumulation.

Power plant-effect snowfall also requires something called an inversion to be present in the atmosphere. That's an increase of temperature with height that in essence caps pockets of air near the surface and prevents them from rising. Otherwise, the warm, moist steam plume would billow aloft and dissipate upon exiting the smoke plume; an inversion traps that moisture near the surface and concentrates it to the point of saturation.

Slaughterhouses

While a bit gruesome, yes, slaughterhouses can, and occasionally do, produce snowfall. Just about anything that spits out steam can. On January 19, 2011, up to 0.7 inches fell in Dodge City, Kansas, where the exhaust from a power plant smokestack combined with that of two slaughterhouses.

Sound-effect snow

No, this one isn't as cool as it sounds. But if you've heard of lake-effect snow, then you'll love sound-effect snow. It's ocean-effect snow that forms because the water in shallow sounds is a bit warmer than the surrounding deeper ocean. When cold air flows lengthwise along the sound, moisture is lifted into the atmosphere. That effect is more dramatic when there is a significant temperature difference between the water and the air above.

Sound-effect snow has happened in Long Island Sound before, and can even bring significant snowfall to Block Island, Rhode Island, as well as Martha's Vineyard, Mass.. Similar sound-effect snow has even been spotted in Pamlico Sound along the Outer Banks of the Carolinas!

Rivers

Under exceptional circumstances and with the right wind fetch, rivers have made their own mini snowstrips before. In November of 2019, the Mississippi River managed to do it near Memphis with cold winds out of the north.

It also happened on January 27, 2017, when the Weather service in the Quad Cities of Iowa and Illinois issued a special weather statement, noting that a west to east oriented stretch of the Mississippi River had provided the necessary moisture to generate its own stationary band of snow.

"Visibilities will drop quickly to less than a quarter of a mile in this squall," the Weather Service wrote. Temperatures at the time were in the 20s.

Tiny lakes

Lake-effect snow on the Great Lakes is one thing. But on much smaller lakes, lagoons and ponds? Yep, apparently it can happen. On January 25, winds out of the northeast generated a band of snow downwind of comparatively mild Lake Tahoe, California. In February of 2020, Lake Lanier in Georgia produced lake-effect snow just northeast of Atlanta.

A number of other small bodies of water across the Carolinas and Tennessee Valley yielded some flurries during that same event.