A strange cloud formation has been baffling residents living in northern California.
The clouds seemed to settle in such a way that there seemed to be a giant hole in the sky near San Francisco on Friday morning.
The phenomenon was observed mainly in Bay Area cities such as San Bruno, San Mateo and Burlingame.
The strange looking clouds caused people to take pictures of strange looking clouds and post them on social networks.
The San Francisco Bay Area sky featured unusual cloud formations early Friday morning
Several people pointed out strange shapes in the sky on social media and posted photos online
Cloud formations are called flake fall and are also known as "perforated clouds".
Something, like an airplane, travels through the cloud layer and interrupts the pressure and humidity inside that layer
When a plane passes, it causes the super-cooled water and ice crystals to evaporate and sublimate as they fall from the cloudy layer. This creates brush-shaped stripes as seen in the holes above
Experts say that the impressive clouds that look like brushstrokes or seashells, even suitable for the coastal region, are caused by a rare, but quite common, atmospheric occurrence.
The chief meteorologist at KRON4, Lawrence Karnow, says that the formation is known as "autumn fall hole" or "perforated cloud".
Clouds can form when the water droplets are colder than the freezing temperature, but they have not yet frozen.
"Super cooled" water droplets need a "reason to freeze", which usually occurs when ice crystals pass by.
As moisture falls, it leaves dry air behind which the hole is produced and, in some cases, an elliptical opening in the cloud.
Many noticed on social networks that there were "spectacular circles in the clouds". One person asked if it was a strange portal
The National Meteorological Service explains that water falls occur when the water temperature in a cloud is below the freezing point, but the small water droplets that make up the cloud have not yet frozen.
The clouds took the form of a giant, dim hole in the sky and many people wondered what exactly they were
A dropping hole is formed when part of the cloud layer forms ice crystals that are large enough to fall like a fall from the fall.
They form in clouds of super cooled water droplets: water less than 0 ° C but not yet frozen.
These water droplets need a small particle to freeze or cool below -40 ° C.
Drilling the aircraft through this cloud layer can cause the air to expand and cool as it passes over the wings of the aircraft or propeller.
This change in temperature may be enough to encourage supercooled droplets to freeze and fall from the cloud layer in this distinctive pattern
Planes that travel through the clouds can often bring these ice crystals with them.
Once the crystals are introduced, the drops of water freeze quickly and begin to fall leaving behind a hole.
The wispy clouds that form in the center of the hole are the falling water particles.
The hole begins to expand outward as the neighboring drops begin to freeze.
It is thought that the passage of airplanes is the reason behind the formation of these clouds, since a drop in pressure caused by their wings or propeller tips cools the air quickly.
Sometimes you see rainbows with autumn fall clouds, thanks to the light that is reflected in the drops of water.
No matter the science, the clouds are extremely beautiful and create some interesting images of the Instagram climate, and a change of the storm clouds that are present on the east coast with Hurricane Florence.
The clouds were so high that people in a large area could see them
The clouds seemed to last several minutes while the formations remained stable giving people enough time to take pictures
Because the clouds were over a heavily populated area, the formation was photographed from several different angles.
The vision conditions were absolutely perfect, and there was not much more in the cloud cover that could obscure the phenomenon.
From the city, and towards the countryside, no matter the location, the clouds made an unusual and welcome sight