Amazing Fallstreak Cloud

Gwyneth Seelinger was amazed by this “funny cloud” that our science contributor David Lynch described as a fallstreak cloud and fallstreak hole. Photo by Gwyneth Seelinger

On Jan 21, 2017, ten-year-old Topanga resident Gwyneth Seelinger saw a “funny cloud” over PCH and took a picture of it. What she captured with her iPhone was one of the best photographs ever taken of a fall streak and a fallstreak hole.

A thin layer of puffy clouds called altocumulus blanketed the area. These are high (about three miles on this day) cold clouds whose water droplets are colder than 32°F but they haven’t frozen yet. Such water is called “supercooled”.

For any number of reasons—a passing airplane, updraft, bit of dust—the water drops suddenly freeze and start growing into very large ice crystals, like snow, which starts falling out of the cloud. These wisps of cirrus clouds are called fallstreaks and appear to hang from the cloud like a beard.

When water freezes, it releases heat that warms the surrounding altocumulus cloud and evaporates the cloud droplets. This leaves a hole in the cloud known as a fallstreak hole.

Gwyneth’s beautiful picture shows that it’s a good idea to take a moment and look around the sky every time you go outside.


By David K. Lynch


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