Planes Flying Into Chicago Made It Snow
They say you should learn something new everyday, so here's your something new for today: airplanes can make it snow!
The science of the event is lost on my slow brain, but suffice it to say the propellers and jet engines and wings combine to seed the clouds as the planes descend through them. Got it? Here's the technical explanation:
As the airplanes descended for landing they flew through water-laden clouds in temperature that were below freezing, the National Weather Service in Grand Rapids, Michigan, said. Ice crystals formed as a result.
This is called inadvertent cloud seeding, according to a study by Andrew Heymsfield and collaborators.
They concluded that aircraft propellers and wings cause the formation of those ice crystals. There are zones of locally low pressure along the wing and propeller tips which allow the air to expand and cool well below the original temperature of the cloud layer, forming ice crystals.
Hole-punch clouds, or canal clouds, can also develop from this type of cloud seeding. Satellite imagery showed the formation of a hole-punch cloud over Lake Michigan on Tuesday.
These rare cloud formations develop in altocumulus cloud layers as airplanes pass through them.
The altocumulus cloud layer is composed of small water droplets that are below freezing, called supercooled water droplets. If ice crystals can form in the layer of supercooled droplets, they will grow rapidly and shrink or possibly evaporate the droplets completely.
Studies, including the one by Heymsfield, have shown that aircraft passing through these cloud layers can trigger the formation of the heavier ice crystals, which fall to earth and then leave the circular void in the blanket of clouds.
I'm willing to believe them.