Rockford, MI (WOOD) — Did you see it? A spectacular cloud formation, known as a fallstreak hole, opened up over the skies of Greenville and metro-Grand Rapids Friday.HOW DO THEY FORM?
Atmospheric conditions were just right on Friday for a fallstreak hole to spread across the sky. These are also known as a “hole punch” cloud, since it looks like a perfect hole has been punched out of a cloud layer.
These form when an ice crystal from a cloud layer higher up in the sky falls into a cloud layer below filled with super-cooled water droplets. Super-cooled water is when water stays in liquid form, even though it’s temperature is technically colder than 32°! This happens frequently to the water droplets in clouds, because the water in the atmosphere is so pure.
Scientifically, the saturation vapor pressure over water is greater than the saturation vapor pressure over ice. This means, if given the chance, super-cooled water droplets will rapidly convert to ice. This is known in the meteorological world as the Bergeron-Findeisen Process.
We see this happening in a fallstreak hole.
When an ice crystal falls down in the sky from a cloud layer at a really high altitude and hits a cloud layer made of super-cooled water droplets, like it did on Friday, an instant conversion takes place.A chain reaction of super-cooled water droplets turning to ice starts erroding a circle in the sky, radiating from where that first ice crystal hit.
The hole grows wider and the ice crystals fall (in a streak) from the center.HOW COMMON ARE THEY?
Fallstreak holes are fairly rare. We don’t see them on a weekly basis, and can go months without having them form in West Michigan skies. They can happen all over the country and are most common during seasons in which the lower levels of the atmosphere are near freezing and the upper-levels of the atmosphere are cold enough for ice crystals.
What made the Dec. 1 fallstreak hole in Greenvillle a bit more rare was the iridescence that formed on the ice crystals streaking down from the center of the hole. Iridescence makes a rainbow like appearance on clouds composed of similarly shaped ice crystals. When the sun hits these crystals just right it creates this additionally beautiful display.
If you grabbed any pictures of a fallstreak hole, be sure to share them with us on Facebook, Instagram, and Twitter. You can contact us on our website with Report It.
>>Photos: Fallstreak hole in West Michigan