How to Read the Weather in the Mountain

Clouds can provide us, in addition to a multitude of sensations, very useful information regarding the meteorological weather that we can find throughout our excursions and outings in the mountains. Knowing if it will rain in the next few hours, if a storm is coming, if the good weather will continue after eating, or if there is a lot of air on top of a peak is information that we can obtain just by looking up.

Although no two clouds are the same, many share features that made their classification possible back in the 19th century. This classification can meet different criteria, but for this article to be helpful we will base ourselves on the visual characteristics of the clouds to learn to identify them and to read the weather in the clouds.

We can group them into three types of clouds depending on the altitude at which they are:

Cloud Classification


They are clouds that usually have a stratum shape, small thickness and wide horizontal extension, with a low density and formed by tiny ice particles. They can appear between 5 and 13 km in height (usually above 8 km). Aircraft condensation trails are also included, although they are artificial.


Located at intermediate levels of the troposphere, between 2 and 7 km.


They occupy low positions, close to the earth's surface and below 2 km of altitude. Made up of water droplets, they can contain ice crystals and snow during the coldest times of the year.

Let's see what each of them tell us:


Cirrus (Ci) or cirros:

Separate clouds in the form of filaments, with a fibrous appearance and a delicate texture. Its white color is due to the fact that they are made entirely of ice and it has a high reflectivity. They acquire stretched or stylized forms as narrow or branched bands.

When they appear in isolation, it means that atmospheric stability is guaranteed in the short term. But if we see them move in one direction in an organized way, in the form of long, somewhat thick bands and covering more and more of the sky, they usually announce a change of time. They are the first outpost of a warm front that will end up covering the sky and leaving weak precipitations. Although, at least until a couple of hours after observing the arrival of these clouds, the weather will remain dry.

 Cirrostratus (Cs) or cirroestrastos:

They are translucent clouds, in the form of an almost transparent and whitish veil, with a fibrous or completely smooth appearance, that totally or partially covers the sky. They usually give rise to halos: a luminous ring that surrounds the sun or the moon in the presence of these clouds.

When a solar halo disappears and the cirrostratus transforms into upper strata, they announce the arrival of a warm front and the possibility of light drizzle. These clouds appear behind the cirrus clouds in the sequence of clouds that precede the arrival of a warm front.

Cirrocumulus (Cc) or cirrocúmulos:

Clouds in the form of a layer or thin blanket, whitish in color and without their own shadows. They adopt waveforms, curls or granules. Formed by ice crystals, they can be of the species: castellanus, floccus, stratiformis and lenticularis.

They are indicative of a certain degree of atmospheric instability.


They are the clouds located in intermediate levels of the troposphere, between 2 and 7 km of altitude.

Altostratus (As) or Altoestratos:

They appear as a large sheet of clouds, bluish gray in color, with a striated, fibrous or uniform appearance. Its thickness is around 3 km on average. From land, through the thinnest areas the solar disk can be distinguished. They are formed by ice crystals at the top, while in the rest of the cloud drops of liquid and sub-melted water and snowflakes mix.

They produce precipitations, in the form of water or snow, normally continuous, but not very intense.

 Altocumulus (Ac) or altocúmulos:

They are shown as a thin layer, white and gray, with shadows. The aspect of the sky is usually that of being paved, forming a kind of honeycomb or a flock of sheep: "abhorred sky."


Ac floccus do not usually cause precipitation; although they are associated with the least active part of a storm, so if they are increasing or if the empty or hollow spaces are welded together to form a uniform blanket, they do indicate a worsening of time, indicating the arrival of a disturbance and medium-term rainfall. 

The Altocumulus castellanus owe their name to their appearance, similar to the battlements of a castle like cloudy towers. Its appearance in the sky in the early hours of the day, when the insolation has not yet heated the air near the ground enough to trigger convection, reveals the existence of atmospheric instability. So if those battlements or towers continue to grow, they will become storms.


As for the Ac lenticularis in a flattened shape (like a lens or duckweed) with well-defined contours, they owe their origin to the action of the wind that shapes them until they are flat. They can appear isolated on a peak, or forming bands of several layers. They are formed in the lee of a mountain range and their formation is due to the deformation suffered by the wind when overcoming a relief. They indicate the presence of strong winds at height or at medium levels. In a mountain range, apart from strong winds at the top, they indicate relatively stable weather on the leeward slopes, where the air humidity will be low. Its evolution usually indicates the distance from a storm.

Nimbostratus (Ns) or nimboestratos:

This is the typical rain cloud. Thick, gray, gloomy-looking cape reveals the presence of a significant amount of water droplets or snowflakes inside. It works by covering the solar radiation, greatly reducing visibility in its vicinity and its persistence manages to considerably reduce temperatures. Although it is considered an average cloud, its base is sometimes below 2 km.

They produce continuous precipitations in the form of water or snow and of moderate amount.


They are those that occupy low positions, close to the Earth's surface and below 2 km of altitude. Made up of water droplets, they can contain ice crystals and snow during the coldest times of the year.

Stratocumulus (Sc) or estratocúmulos:

Bench, sheet or layer of gray or whitish clouds that often reaches a great extension. They present the appearance of a sea of scrambled clouds, formed by globular shapes packed together. They are associated with the retention of cloudiness in some slopes of mountain ranges.

They give rise to light rain, drizzle or granular snow. Its appearance combined with cumulus and cirrus in height is associated with the days after the entrance of a cold front.

Stratus (St) or strata:

Gray cloud layer and uniform base. Its thickness is small compared to the extension they reach horizontally. A particular case of strata would be the mists, whose base coincides with the Earth's surface.

Their presence is a clear indicator of atmospheric stability, although some authors suggest that they sometimes give rise to drizzles, never to rains, in which case they would be nimbostratus.


As its name suggests, this cloud family evolves growing mainly vertically, from bottom to top. Its greater or lesser growth is defined by the degree of atmospheric instability and by the thrust of air ascents (convection), favored by heat (mainly at noon).

Cumulus (Cu) or cúmulos:

They are clouds that appear isolated, they are usually dense and with well-defined contours, presenting protuberances at the top that give them the appearance of cauliflower. The immaculate whiteness of its upper part (as long as it is illuminated by the sun) contrasts with its dark base. They tend to form earlier on the east or southeast slopes, which overheats more quickly when facing the sun. Its base, in summer and with stable weather, is between 3,000 and 3,500 m, and around 2,000 or less when the weather worsens or is unstable. Depending on the vertical development and size they reach, we can identify 3 cumulus species: humilis, mediocris and congestus.

Cumulus humilis:

They are small in size and totally white, the typical 'cotton clouds'. If we observe them during a noon day we can be calm, they are normally associated with stable and dry weather, they are the clouds of good weather. The cloudiness does not grow since the surface air mass does not provide too much humidity and the temperatures at height are relatively high.

Cumulus mediocris:

Of intermediate size and dark base, if the forecasts indicated unstable weather and in the morning we already observed clouds of vertical development that are growing with the passage of minutes, they are a clear sign of bad weather. It means that in upper layers of the atmosphere there is cold air, causing the formation of cloudiness in the early hours. By mid-morning or noon these cumulus will have been transformed into cumulus congestus, and in the early afternoon the storm will surprise us in the mountains.

Cumulus congestus:

They are large clusters. They indicate a worsening of time in the very short term. It is the cloud prior to the formation of a storm. They can produce abundant rainfall, especially if they remain immobile. The intensity of the precipitations will come determined by the continuous contribution of humid air (and therefore warm) coming from low layers. In maritime areas, with an extra supply of humidity, they can leave very intense rains without developing as cumulonimbus.

Cumulonimbus (Cb) or cumulonimbos:

They are gigantic, dense cloud structures with very important vertical development (their top can exceed the troposphere level, about 20km). It is no longer shaped like a cauliflower, but a mountain with imposing towers. The upper part is totally or partially flattened, often taking the shape of an anvil (due to prevailing winds at height). Its base is dark, gloomy and threatening in appearance. They come from the formation of a cumulus congestus and it can be difficult to differentiate from each other especially when the typical upper anvil has not yet been created.

It is the storm cloud, they are usually accompanied by an electrical device. Below them appear torn clouds and heavy rainfall and showers, in the form of rain or accompanied by hail.



This is the name given to the very bright orange or reddish hues that occur in clouds such as stratocumulus clouds when the sun is placed a few degrees above or below the horizon. This occurs at sunrise or sunset, and is caused by a light reflection effect. In general, they are indicating that a front is moving away, improving the time in the immediate hours. However at high altitudes the wind can blow with moderate or even strong gusts.

The arreboles can appear with different clouds, so we must take into account their origin to see if the weather improves or worsens. If they are observed after the passage of a front, it will improve. They can also be associated with storm remnants (anvil remnants). If the cloudiness precedes a theoretical stable period of time, gradual worsening is possible, since in this case they indicate the proximity of a front.

Source: montanasegura.com

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