How high-flying aircraft can cause it to Snow..

Aeroplanes passing through clouds can make it snow, according to new research.
Scientists have long been baffled by strange-looking circular clouds known as hole-punch or channel clouds.
These strange meteorological phenomena appear in high-altitude clouds which are composed of both ice crystals and super-cooled water droplets – water that is below the freezing temperature but still exists in liquid form.
Now a team of researchers in the US have found strong evidence that aeroplanes passing through these clouds can make the liquid water droplets freeze and immediately fall as snow.

A stunning shot of a hole-punch clouds which occurs at high altitudes as water droplets freeze

Scientists have now linked this unique sight to aeroplanes and snow

Andrew Heymsfield of the National Centre for Atmospheric Research and colleagues flew a research plane through the snow produced by a hole-punch cloud west of Denver International Airport in 2007.

They discovered that radar was picking up the signal for snowflakes in their wake.
Video from the flight showed a hole in a patch of altocumulus clouds, and two inches of snowfall directly below the hole
The researchers examined flight records for the nearby airport and linked the hole and the snow to two commercial turboprop aircraft that had taken off an hour earlier.
The supercooled droplets freeze after passing over the jet planes’ wings, Heymsfield told Wired magazine.
'We know exactly which aircraft produced the holes,' he said. 'Researchers had previously linked a lot of snow to propeller aircraft, but they hadn’t made the connection to jet aircraft.'
Not all flights through banks of clouds will produce snow as the clouds with super-cooled droplets only form at certain altitudes.