Recently we looked at windfarms and microclimatology, and the effect they can have on weather and bad journalism. Today, some neat microclimatology that comes to us from O'Hare. In the animated GIF below from the Milwaukee NOAA office (h/t Paul Douglas, ALM), you should see what looks like a smoke ring pop up near the airport:

O'Hare airplane halo

Here's what happened:

We've seen this before where the exhaust particles from the aircraft feed/seed the clouds and coalescence accelerates, resulting in the development and fallout of ice crystals. Doppler radar can detect these ice crystals along with precipitation.

I think it's an example of, or related to, the "hole-punch" cloud phenomenon, a widely observed but little-studied formation until a 2011 Science paper:

The effect is similar to cloud seeding, which has been used in the past to influence the amount of precipitation falling from a cloud. New research now shows that numerous private and commercial flights have been drilling holes and canals through clouds all along, influencing the snow and rainfall below them.


The inadvertent cloud-seeding effects described in the report are facilitated by the expansion and cooling of air behind a propeller aircraft’s engine blades and over aircraft wings, when supercooled cloud temperatures are about -10 degrees Celsius and below. The associated drops in temperature can be sufficient to spontaneously freeze the supercooled cloud droplets and form ice crystals, which then grow at the expense of the water droplets. The process snowballs—literally—to produce a hole or a canal in the cloud layer that can continue expanding for hours, increasing precipitation in and below the cloud.


So, it seems that aircraft coming and going from airports around the world can inadvertently seed clouds in this fashion to produce more snow inside the clouds and on the ground below, the researchers report. By punching holes or drilling canals through cloud covers, private and commercial flights alike could be responsible for increased snowfall around major airports.

Hole-punch clouds are really cool looking.

By the way, if anyone would like to use this as evidence against global warming, a chemtrail conspiracy, Project Cloverleaf, or something something HAARP, I could use the traffic.

At the Atlantic Cities, John Metcalfe put together a history of Chicagoans injured by falling ice. I couldn't find much in the way of official statistics here or in other American cities, but I did find a collection representing the diversity of falling-ice-signs in Chicago.