Is your sky filled with grey? Does it look like some celestial prankster spread out a thick blanket that extinguished sun? Don't worry. The sun is still there. It continues to shine despite the fact that you can't see it.
There are many different types of clouds. The one that hovers close to the ground and sprawls out across the entire sky is a stratus cloud. The word stratus comes from a Latin root that means layer. A typical stratus cloud forms close to the ground, and presents itself as a drab, featureless sheet. Although it may seem like a solid lid over your head, the cloud is actually insubstantial, comprised of tiny water droplets and ice particles. You may have even walked through a stratus cloud. When one sits on the ground, we call it fog.
Clouds are ever changing, and the low-lying stratus is no exception. A stratus cloud may break up into a cluster of fragmented pieces, gain some puffiness, and expose small patches of blue sky in the gaps. At this stage of cloud evolution, the cloud is called a stratocumulus.
An altostratus cloud is similar to the undifferentiated stratus cloud, but it forms higher in the atmosphere, typically above 6,500 feet. Altostratus is often a bit thinner than the lower-forming stratus. It can still conceal, or partially conceal, the sun during the day and the moon at night, but you can often still perceive the locations of these objects in the sky. That is unless the altostratus cloud thickens and transforms itself into the darker nimbostratus. When that happens, prepare for rain or snow.
Another form of cloud layer, the cirrostratus, can develop at soaring elevations—16,500 feet and higher. When cirrostratus covers the sky with a thin veil, sometimes the covering is so diaphanous a casual glance won't even detect it. The ice crystals of which it is comprised, however, can reveal its presence by encircling the sun and moon in halos of white or rainbow-like light.
The original version of this article appeared in the February 2016 issue of Observations: A Pier Press® Newsletter. It included links to additional resources about clouds. You can access the archived issue here, and if you're not already a subscriber, click here to sign up. It's free. You can also order a copy of The Cloudspotter's Guide by Gavin Pretor-Pinney from the Pier Press Bookstore.