- Airplane traffic is causing light snowfall in Chicago via a phenomenon called ice nucleation.
- The same idea is used to make snow, both with machines and with "private weather modification" services.
- This phenomenon can also cause hole punch clouds and fallstreak holes.
Chicago’s chapter of the National Weather Service has suggested that light snowfall in the metro area is being caused by airplane traffic.
Light snow near Chicago? We think this is being caused by airplanes descending into O'hare and Midway airports this evening. Be warned: there's lots of science ahead in the attached graphic! #science #snow #ILwx pic.twitter.com/L1SFioO631— NWS Chicago (@NWSChicago) January 27, 2020
Unlike chemtrails, this science is real. The infographic suggests that when water in the atmosphere is pure enough, it doesn’t freeze until -40 degrees Celsius/Fahrenheit (this is where they converge), and our current cloud cover is well above that. But the supercooled water will freeze if it’s seeded by microscopic particulate in the air, like those in airplane exhaust. Combined with the air turbulence created by moving airplanes, the supercooled water can freeze to the particulate then drift and form light snowflakes in the turbulent air.
The same phenomenon is responsible for delightfully named hole punch clouds, where supercooled water clouds are “punched through” by aircraft and create The Truman Show-like targeted rain- or snowfalls beneath them. They look like a reverse contrail. More accurately, they’re like foggy windows that someone draws on using a finger, where condensation spreads out evenly until it is disturbed by intruding forces.
When supercooled water coalesces around tiny particles and forms ice, this is called ice nucleation. If this sounds like how pearls form, that’s because it is—and the same way pearls can be cultured on purpose, clouds can be artificially seeded. Euphemistically called “private weather modification,” cloud seeding is used by different groups around the world to try to cause more desirable weather.
Within the U.S., it’s used to drum up fresh powder in Colorado and to fill reservoirs in the Southwest. Pew Research says that while it’s hard to evaluate how effective these private weather modification technologies are, they’re also very cheap, so municipalities and other local governments figure it’s worth a try.
If you’ve ever dropped a Mentos into a bottle of Diet Coke, you’ve observed another example of nucleation: the seeding “impurities” in this case are the microscopic surface bumps on the Mentos candy. People who tap cans of soda hoping to release the carbonation are trying to do the same thing, and when a glass of beer has trails of bubbles up its side, this indicates tiny impurities of dirt or other particulate acting as catalysts.
Something can also happen called seeder feeder, where not only is a supercooled cloud “seeded” by something, but the precipitation then falls through a second cloud layer and is “fed” by it. The surface beneath the second cloud layer will have more resulting precipitation than areas with just the one seeded cloud layer.
Between Midway Airport and O’Hare Airport, much of Chicago is covered by flight paths. O’Hare has about 2,400 flights (incoming and outgoing) per day and Midway adds about another 10 percent of that number. But the Chicago office of the National Weather Service says the airplane-caused snow is unlikely to stick, let alone accumulate.
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