Identifying the types of Cloud present

Factors affecting cloud appearance

The appearance of a cloud is affected by the amount of light that is reflected, scattered and transmitted by the cloud. This light comes mainly from the sun or moon or from the sky; it may also come from the surface of the earth, and is particularly strong when sunlight or moonlight is reflected by ice-fields or snow-fields.

Haze

When there is haze between the observer and the cloud it generally diminishes cloud brilliance. Haze reduces the contrasts which reveal the shape, structure and texture of a cloud. Haze makes distant clouds look yellow, orange or red.

Night-time

On a moonlit night, clouds are visible when the moon is more than a quarter full. In its darker phases the moon is not bright enough to reveal clouds far from it, especially thin clouds. On a moonless night, clouds are generally invisible but their presence may be deduced from some or all stars being concealed, or from artificial lighting (illumination from large cities, towns, fires, etc which tend to give the base of clouds an orange glow).

Sun or moon behind cloud

The further thin cloud is away from the sun or moon the darker the cloud will appear. With thick clouds there is only a slight change in appearance with distance.  Sometimes the edges of a thick cloud may be brilliantly illuminated. Thick Cirrus type clouds are always brilliantly white unless the sun or moon is behind them when they will show shading.

Cloud opposite sun or moon

Light is reflected from the cloud to the observer. The thicker the cloud the more light is reflected and the more brilliant the cloud appears. When sufficiently thick and deep, clouds can reveal shades of grey revealing more of the cloud profile.

Thick Cirrus type clouds are an exception to the above. They will appear brilliantly white and show no shading with the sun or moon opposite.

Sun high above the horizon

Clouds or portions of clouds in direct sunlight appear white or grey. Parts receiving light mainly from the blue sky (those closer to the ground) are bluish-grey. With weak illumination the clouds tend to take the colour of the surface below them.

Sun approaching the horizon

The colour of the sun may change from yellow through orange to red, and the sky in the vicinity of the sun and the clouds may show a corresponding colouration. The colours may still be influenced by the blue of the sky and the surface colour below, and the effect also varies with the height of the cloud.

Sun close to or below the horizon

High clouds may still look white whilst middle level clouds exhibit a strong orange or red coloration, and very low clouds, in the shadow of the earth are grey. These differences help to obtain an idea of the relative heights of the clouds.  Note, however, that clouds at the same level appear more red when they are seen away from the sun than when viewed toward it.