Altostratus is a mid-level fog
Štěpán Šubík last edited by iblfilip
In the previous post, we mentioned the first mid-level cloud - Nimbostratus. Now is time to reveal another mid-level cloud - Altostratus.
As you may have recognized, "stratus" means cover or spreading in Latin. Therefore, every cloud that has "stratus" in its name is large and covers the whole sky. Stratus covers the low-level, Nimbostratus goes from low-level to mid-level and Altostratus is a layer in the mid-level troposphere.
Altostratus is greyish or bluish cloud sheet that can look uniformly or it can have a fibrous or striated appearance. Some parts of the cloud are thin enough just to reveal the Sun or even the Moon. As compared to Stratus, Altostratus has some shading and is not as white as Stratus may be when seen towards the Sun. And compared to Nimbostratus, through Altostratus you can see the Sun (its thinner), it has a lighter shade of grey and less uniform base.
Altostratus is created from cirrostratus, when it gets thicker or nimbostratus when it gets thinner. In some cases, Altostratus can form from Altocumulus or even from Cumulonimbus (when the middle part of the cloud expands).
When the Altostratus is torn apart, shaped or weak, it means that a weakening warm front is coming. Otherwise, it means an occluded front. Precipitation is possible in thicker clouds and when it is persistent, the cloud is reclassified as Nimbostratus.
Have you seen one of them? Send your photos!