7 Rare clouds types | Amazing Weather

Mammatus cloud

Most of us see clouds every day, but only very occasionally will you be lucky enough to spot one of these 7 particularly rare types – some of which can only be seen in very specific circumstances or locations.

Noctilucent clouds

One of the rarest and most beautiful of all cloud types. They are found at very high altitudes – up to around 250,000 feet Visible on clear, summers nights between 45 °N and 80°N latitude ,they appear illuminated by a blue or occasionally red or green light. We still do not know much about how they are formed, but they are thought to be made up of ice crystals.

Kelvin-Helmholtz clouds

They can sometimes be seen as far as 60 miles downwind of the mountains that formed them. An extremely rare phenomenon, where clouds form as a billowing wave pattern Occurs when there is a strong vertical shear between two air streams. This causes some winds to blow faster at the upper level, than at the lower level.

Mammatus clouds

Bulge or pouch shaped, they’re usually seen emerging from the anvil at the top of cumulonimbus clouds. Formed by turbulence, they are one of the few clouds that come from sinking, rather than rising air.

Lenticular clouds

Usually formed behind hills or mountains, where the air is stable and winds are blowing from a similar direction. These tall geographic features interrupt the wind, the airflow undulates and condenses into these disc shaped clouds.

Funnel clouds

Cone shaped clouds which extend from the cloud base, but never actually touch the ground. Formed in the same way as a tornado around a small area of intensely low pressure. If a funnel cloud reaches the land it becomes a fully fledged tornado and if the funnel cloud reaches the surface of a body of water, it becomes a waterspout.

Fallstreak Hole clouds

Also known as a hole punch cloud – they form when part of the cloud layer turns to ice crystals which are large enough to fall. Water droplets in the cloud, cooled below 0°C but not yet frozen, will freeze if they find a particle to freeze on to or are cooled to below -40°C. Aircraft can cause this to happen by making the air expand & cool as it passes through the cloud

Arcus cloud

Formed when warm air within a storm cloud is pushed up from the ground by the cold air exiting downwards. Unattached to the storm cloud they are known as roll clouds, but when attached they are called shelf clouds.

Noctilucent Cloud Display over NE England June 2019

noctilucent clouds over durham city Noctilucent Clouds over Durham City, June 17th/18th 2019 by Mike Ridley Photography

Some of you eagle-eyed skywatchers will have noticed a ghostly glow in the sky on the way back from the pub in recent days. Was it real? Was it just an illusion caused by too much Gin? No, what you saw was real and is called ‘Noctilucence’. It is a spectacular display of very high clouds.

Noctilucence is exhibited by clouds that shine at night (Noctilucent means ‘night shining’ in Latin). Noctilucent Clouds exist in the upper atmosphere (Mesosphere), at a height of around 50 miles. They are composed of ice crystals and can only be seen in astronomical twilight. That means they are best seen in the summer months, but they are too faint to be seen in daylight. They require moisture, dust and very cold temperatures (less than -120 degC) to form. The Mesosphere is at it’s coldest in the summer months, so favours their formation.

The clouds shine on summer nights when the sun is below the horizon at ground level, whilst up at 50 miles the noctilucent clouds are still in the sunlight. The whispy clouds seem to glow in this ghostly manner. They are a comparatively recent discovery and are not fully understood, but they seem to be occurring more often and with increasing brightness.

There have been some fantastic photos posted on the internet in the last week or so, but the best I have seen relevant to us is from Mike Ridley who took this superb composite photo over Durham City from Whinney Hill on 17th/18th June 2019.

Here’s Mike’s link.

Mike Ridley Photography

noctilucent clouds by mike ridley photography Noctilucent Clouds over Durham City, June 17th/18th 2019 by Mike Ridley Photography