Why Power Plants Are Acting Like Giant Snow Machines


Human activity can modify weather and climate in many different ways. Cities tend to be warmer than rural areas because of the urban heat island associated with buildings, paved surfaces and lack of trees. Large regions of impervious surfaces, like mall parking lots and interstate highways, can increase rainwater runoff while reducing infiltration into soil. These process make urban flooding worse. Irrigated agricultural regions have also been shown to modify local microclimates. My colleague Roger Pielke, Sr. just recently shared an article about how the nation’s cornbelt is affecting rainfall. Recently, there have been several cases of industrial plants producing their own snow. Why is that happening?

A plume of snowfall caused by an industrial plant near Norfolk, NebraskaNWS Omaha Twitter site

Before answering that question, it is instructive to review a recent social media post by the National Weather Service (NWS) Omaha/Valley Nebraska,

It’s been confirmed that this snow band is originating from two plants in Norfolk. The steam produced there is essentially acting to add moisture and warmth to the clouds which is causing the snow downwind. Had reports of large flakes under the band and up to 1 inch of new snow accumulation.

Anthropogenic generation of snowfall  is actually more common than you think. NOAA Storm Prediction Center Meteorologist Roger Edwards tweeted, “Localized #snow-seeding effects such as this, whether from stack plumes or ski-area machines, are fairly common. This one (graphic above), however, is remarkably lengthy, well-defined and persistent in radar imagery.” The hydrometeor classification algorithm in the NWS Dual-Polarization/Doppler Radar system clearly indicates a plume of snowfall downwind of the two industrial power plants (graphic above).

So how does this happen? Typically, steam from an industrial or power plant will ascend into the atmosphere and evaporate. After all, it is actually small droplets of water. On this particular day (December 3rd, 2018), the atmospheric snow-making machine was set up perfectly for this process to happen. First, I should explain how snow is typically formed. Clouds will often be a mixture of super-cooled water droplets and ice crystals.

Even though it is raining where you are, it probably started as snow. In many places, the Bergeron or “cold rain” process is responsible for the formation of rain (even on a hot summer day). Clouds are often a mixture of ice crystals and super-cooled water drops, and some interesting things happen because of that fact. The College of Dupage website has an excellent discussion of how I would describe the process:

From the perspective of the supercooled droplets, the air is in equilibrium at saturation, but from the perspective of the ice crystals, the air is supersaturated. Therefore, water vapor will sublimate on the ice crystals. Since the amount of water vapor in the air has decreased, and from the perspective of the supercooled water droplet, the air is subsaturated, the supercooled water will evaporate until the air once again reaches saturation. The process then continues.

As ice crystals (snow) grow at the expense of the supercooled water, they grow larger by clumping together with other crystals or gaining mass through accretion of supercooled water as they fall. On this day, steam from the plants interacted with the ice crystals and supercooled liquid. Weather balloon data also indicated that a shallow layer of cold air was in place. These conditions were ideal for giving the natural snow-making process a boost. CIMSS meteorologist Scott Bachmeier at the University of Wisconsin tweeted,

Very cool — it appears that the Norfolk plant emissions caused the supercooled clouds to glaciate and produce snow (thereby eroding the cloud, much like what happens with an aircraft “fall streak cloud”….However, there were also plumes in Greeley, Howard and Polk counties that did not produce this effect. Wonder how those other plumes were different? Different emissions? Varying stack heights?

If you look at NOAA satellite imagery from the VIIRS instrument (below), you can see what Scott is talking about. There were other plumes that did not produce a robust snowfall plume. I suspect some future graduate student will figure out why.

Plumes over Nebraska on December 3rd from VIRSS satellite instrument.Scott Bachmeier/CIMSS

Capital Weather Gang recently wrote about industrial snow plumes near Chicago, and I even co-authored a scholarly paper on an industrial-slaughterhouse snow event near Dodge City, Kansas several years ago. Anthropogenic effects on weather and climate extend far beyond carbon dioxide in the atmosphere.

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