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Few words about clouds and predicting weather

Tags: cloud

When you spend time hiking, trekking or just walking for a long time, it is useful to know what kind of weather you can expect. In nowadays easiest way to check for weather is to go online and visit one of many weather forecasting web pages (my favourite: Norwegian Meteorological Institute). But as an outdoor type of person, you should know how to predict weather even without the internet. One of that ways is knowing what clouds above you are telling you.  As I am not a meteorologist and as I am not fully competent to talk about this topic, I will only handle the subject superficially. If you want you can deepen your knowledge more and this text can be your kick starter for doing so. Please let me know about any improvements or new things that you learned and could be used in this post.

There are a lot of subtypes of clouds and I will not go and explain every single one. From this text, you will learn what is what in the sky and what in general to expect from clouds above you (just shadow, storm, rain….).

According to The National Weather Service (NWS)  there are 10 basic types of clouds that are separated into three categories depending on what height clouds are formed. So we have:  High clouds, Mid clouds and Low clouds.

 

High clouds

All high clouds have their bases above 6.000m, and all of them are a type of cirrus cloud.
In this category, we have Cirrus, Cirrostratus and Cirrocumulus.

Cirrus

Height of base: 5.500 – 12,000 m;
Shape: Layered, tufty or patchy;
Precipitation: None, but indicates a change in the weather;

Cirrus clouds are short, detached, hair-like clouds that are formed in high altitudes. Cirrus clouds are wispy with a silky sheen or look like tufts of hair. In the day time, they are whiter than any other cloud in the sky.

   Image source: Clouds-online.com

When these clouds cross the sun’s disk they hardly diminish its brightness. Before sunrise and after sunset, cirrus is often coloured bright yellow or red.

They often form before a warm front where the air masses meet at high levels Cirrus clouds indicate a change in the weather. These clouds produce precipitation, however, it never reaches the ground because it evaporates on its way to the ground forming new clouds.

There are 5 types of Cirrus clouds:

  • Cirrus fibratus – Thin and fiberous, cirrus fibratus are often aligned with the high altitude wind direction, making for white parallel stripes which streak across the sky. These are the most common type of cirrus cloud;
  • Cirrus uncinus –  They are famous for looking like a horse’s tail;
  • Cirrus spissatus – These clouds sit right at the top of the troposphere;
  • Cirrus floccus – Ragged cirrus patches which are much larger than cirrocumulus floccus;
  • Cirrus castellanus – More vertically developed than cirrus floccus, cirrus castellanus have turret like tops and are taller than they are wide.

Cirrostratus

Height of base: 5.500 – 12,000 m;
Shape: Layered;
Precipitation: None;

Image source: Clouds-online.com

Cirrostratus are transparent clouds, which cover large areas of the sky. They sometimes produce white or coloured rings, spots or arcs of light around the sun or the moon that are known as halo phenomena. Sometimes they are so thin that the halo is the only indication that a cirrostratus cloud is in the sky.

Though cirrostratus itself does not produce precipitation, it can indicate whether or not precipitation is likely. If cirrostratus nebulosus exists in the sky it is likely that and the incoming warm front will be persistent rain within a day, though if cirrostratus fibratus is spotted, Stratus may proceed it, bringing only light drizzle.

These clouds can span thousands of miles and may be smooth or fibrous. Shadows will normally be cast by the sun when shining through these clouds, which can help distinguish them from similar altostratus clouds.

There are 2 types of Cirrostratus clouds:

  • Cirrostratus fibratus – Similar to cirrus, but with more consistency; 
  • Cirrostratus nebulosus – A uniform veil-like layer covering the sky.

Cirrocumulus

Height of base: 6.000 – 12,000m;
Shape: Layers or patches of cells;
Precipitation: None;

Cirrocumulus clouds are made up of lots of small white clouds called cloudlets, which are usually grouped together at high levels.

Image source: Clouds-online.com

Composed almost entirely of ice crystals, the little cloudlets are regularly spaced, often arranged as ripples in the sky.

Precipitation from cirrocumulus clouds never reaches the surface, meaning that these clouds are usually associated with fair-weather. However, their appearance can often prelude stormy weather.

There are 4 types of Cirrocumulus clouds:

  • Cirrocumulus stratiformis – Flat sheets or patches of cirrocumulus with fine separation leading to a fish scale like appearance;
  • Cirrocumulus lenticularis – High level icy lenses. These are often larger than the usual altocumulus cloudlet, with a rounded shape;
  • Cirrocumulus floccus – Fluffy tufts of cirrocumulus, with a more ragged appearance than other species;
  • Cirrocumulus castellanus – Taller than they are wide, cirrocumulus castellanus resemble tiny towers sitting high in the sky;

 

Mid clouds

All mid clouds have their bases between 2000m and 7000 m.
In this category, we have Altocumulus, Altostratus and Nimbostratus.

Altocumulus

Height of base: 600 – 5,500m;
Shape: Bands or areas of individual cells;
Precipitation: None;

Image source

Altocumulus clouds are small mid-level layers or patches of clouds, called cloudlets, which most commonly exist in the shape of rounded clumps. There are many varieties of altocumulus however, meaning they can appear in a range of shapes. Altocumulus are made up of a mix of ice and water, giving them a slightly more ethereal appearance than the big and fluffy lower level cumulus.

Mostly found in settled weather, altocumulus cloudlets are usually composed of droplets, but may also contain ice crystals. Precipitation from these clouds is rare, but even if rain does fall it doesn’t reach the ground. Some types of Altocumuls can lead to forming stormy clouds such as cumulonimbus.

There are 4 types of Altocumulus clouds:

  • Altocumulus stratiformis – The most common type of Altocumulus, looking like flat-bottomed puffy clouds packed tightly together but separated by small rivers of sky;
  • Altocumulus lenticularis – One of the most spectacular cloud types and they are lens-shaped clouds that form over hilly areas. Sometimes referred to as ‘spaceship clouds’ they often resemble the shape of a UFO;
  • Altocumulus castellanus – An indicator of instability, Altocumulus castellanus towers can lead to the formation of cumulonimbus thunderstorms. These are more puffy looking and are taller than they are wide, making them stand out from other altocumulus varieties;
  • Altocumulus floccus – Often spotted alongside altocumulus castellanus, altocumulus floccus are made up of slightly smaller, more ragged cloudlets;

Altostratus

Height of base: 2.000 – 6,000m;
Shape: Layered and featureless;
Precipitation: None;

Altostratus are large mid-level sheets of thin cloud. Usually composed of a mixture of water droplets and ice crystals, they are thin enough in parts to allow you to see the sun weakly through the cloud. They are often spread over a very large area and are usually featureless.

Altostratus clouds often form ahead of a warm or occluded front. As the front passes, the altostratus layer deepens and bulks out to become Nimbostratus which produces rain or snow. As a result, sighting it can usually indicate a change in the weather is on the way.

Altostratus clouds are featureless with little character, so there are no special types or categories of this clouds.

Nimbostratus

Height of base: 600 – 3,000m;
Shape: Bands or areas of individual cells;
Precipitation: Continuous rain or snow likely;

Nimbostratus clouds are dark, grey, featureless layers of clouds, thick enough to block out the sun. Producing persistent rain, these clouds are often associated with frontal systems provided by mid-latitude cyclones. These are probably the least picturesque of all the main cloud types.

Image source 

These mid-level clouds are often accompanied by continuous moderate rain or snow and appear to cover most of the sky. Nimbostratus will often bring precipitation which may last for several hours until the associated front passes over.
If there is hail, thunder or lightning present it is a cumulonimbus cloud rather than nimbostratus.

Nimbostratus clouds are featureless, very dense and have little characterization so there are no special types or categories of this clouds.

Low clouds

All low clouds have their bases up to 2.000m.
In this category, we have Cumulus, Stratus, Cumulonimbus and Stratocumulus.

Cumulus

Height of base: 400 – 2000m;
Shape: Cauliflower of fluffy;
Precipitation: Mostly none but possible occasional rain or snow showers;

Image source

Cumulus clouds are detached, individual, cauliflower-shaped clouds usually spotted in fair weather conditions. The tops of these clouds are mostly brilliant white tufts when lit by the sun, although their base is usually relatively dark.

Mostly, cumulus indicates fair weather, often popping up on bright sunny days. Though if conditions allow, cumulus can grow into towering cumulus congestus or cumulonimbus clouds which are capable of producing showers.

There are 4 types of Cumulus clouds:

  • Cumulus humilis – these are wider than they are tall, often numerous in the sky and indicate fair weather conditions;
  • Cumulus mediocris – these are as wide as they are tall and are usually seen amongst a variety of other cumulus variations;
  • Cumulus congestus – these are taller than they are wide, looking like long chimneys capable of producing light showers;
  • Cumulus fractus – these are the broken remnants of cumulus clouds that are breaking up or ‘dissipating’.

Stratus

Height of base: 0 – 2000m;
Shape: Layered;
Precipitation: Possible light rain or drizzle;

Stratus clouds are low-level layers with a fairly uniform grey or white colour.

Image soruce: http://www.metoffice.gov.uk/learning/clouds/low-level-clouds/stratus

Often the scene of dull, overcast days in its ‘nebulosus’ form, they can persist for long periods of time. They are the lowest lying cloud type and sometimes appear at the surface in the form of mist or fog.

Stratus are usually accompanied by little to no rainfall, however, if they are thick enough they can produce light drizzle. This drizzle can also fall in the form of light snow if cold enough.

There are 2 types of Cumulus clouds:

  • Stratus nebulosus – This is a featureless, dark layer which is capable of producing drizzle.
  • Stratus fractus – This is a stratus layer which is starting to break up or ‘dissipate’.

 

Cumulonimbus

Height of base: 350 – 2000m;
Shape: Fibrous upper edges, anvil top;
Precipitation: Heavy rain and thunderstorms !!!;

Image source

Cumulonimbus clouds are menacing looking multi-level clouds, extending high into the sky in towers or plumes. More commonly known as thunder clouds, cumulonimbus are the only cloud type that can produce hail, thunder and lighting. The base of the cloud is often flat with a very dark wall like feature hanging underneath, and may only lie a few hundred feet above the Earth’s surface.

Cumulonimbus clouds are associated with extreme weather such as heavy torrential downpours, hail storms, lightning (and even tornadoes in the USA). Individual cumulonimbus cells will usually dissipate within an hour once showers start falling, making for short-lived, heavy rain. However, multi-cell or supercell storms contain many cumulonimbus clouds and the intense rainfall may last much longer. 

There are 3 types of Cumulonimbus clouds:

  • Cumulonimbus calvus – The top of the cumulonimbus is puffy, like a cumulus cloud;
  • Cumulonimbus capillatus – The top of the cloud is fibrous but relatively contained.  Usually indicating rain has begun or will begin soon;
  • Cumulonimbus incus – The top of the cloud is fibrous and anvil shaped as the cloud has continued to grow. If the cloud reaches the top of the troposphere and still wishes to grow, it must do so outwards, creating the picturesque anvil or ‘incus’;

 

Stratocumulus

Height of base: 360 – 2000m;
Shape: Cumuliform “lump” at base;
Precipitation: Mostly none, but possible light rain or drizzle;

Image source

Stratocumulus clouds are low-level clumps or patches of cloud varying in colour from bright white to dark grey. They are the most common clouds on earth recognised by their well-defined bases with some parts often darker than others. They usually have gaps between them, but they can also be joined together

Stratocumulus clouds can be present in all types of weather conditions, from dry settled weather to more rainy conditions, but they themselves are often not the reason for rain. Stratocumulus are often mistaken for rain clouds, when in reality it is quite rare to get anything more than the lightest drizzle from them, if anything at all.

There are 4 types of Stratocumulus clouds:

  • Stratocumulus stratiformis – The most common cloud type across the globe, these are essentially flat based layers of cloud often with a few cracks between;
  • Stratocumulus cumulogenitus – These form when rising cumulus clouds encounter a temperature inversion and spread outwards clumping together;
  • Stratocumulus castellanus – These are thicker, more drizzly stratocumulus clouds. Turreted tops form when convection initiates through the stable layer allowing stratocumulus to grow upwards, potentially leading to the formation of cumulus congestus or even cumulonimbus.
  • Stratocumulus lenticularis – The rarest variety of stratocumulus. They are often spotted in hilly locations. Very different in appearance to the more spectacular altocumulus lenticularis, they form when hills produce atmospheric waves, which contribute to their lens-like shape.

 

Conclusion

So, there you go, now you have a list of all standard clouds in the sky. You should not expect that after reading this post, you will know every time what is which cloud above you. But you will know at least difference between stormy Cumulonibus and “harmless” Cirrus… Also, don’t forget that high in the mountains weather changes much faster than in regions that are far away from mountains. Use your common sense when planning your hikes and never underestimate mountain and weather.  Also, if you would like to correct or add changes to above list, please contact me and I will probably include those changes in this text.

The post Few words about clouds and predicting weather appeared first on OfficeHiker.



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