Clues on Cloud Classification

Did you look up in the sky this week and see some of those three basic cloud types I mentioned last week – cumulus, cirrus, or stratus?  Perhaps your sky was completely clear and perfect for stargazing all week.  However, it is much more likely that you saw clouds at some point this week that didn’t quite fit into one of those three basic types.  These three basic types were named by Luke Howard in the 1800s as part of his original cloud classification scheme, but in our modern classification scheme they are best thought of as the three basic forms clouds can take.

In our modern classification scheme, we classify clouds into ten genera, which are all just variations or combinations of the three basic forms we discussed last week (cumulus, cirrus, and stratus).  Although they may be a bit cumbersome at first, knowing just these ten genera will help you to better understand what is going on in the world around you.  Low level clouds that sit below 6,500 feet above ground are cumulus, stratus, or stratocumulus (which looks like a layer of flattened out cumulus).

Mid-level clouds that sit between 6,500 and 20,000 feet are classified as altocumulus, altostratus, or nimbostratus.  The prefix “alto-“ comes from the Latin word meaning high (our word “altitude” comes from the same root), so altocumulus is just high cumulus.  The prefix “nimbo-“ means rain in Latin, so nimbostratus is essentially raining stratus.  High clouds sit at approximately 20,000 feet and can be cirrus, cirrostratus, or cirrocumulus.  Cirrocumulus clouds look like tiny puffs clustered together or arranged in rows.  Cirrostratus clouds are sometimes so thin and transparent that we do not even realize there’s a cloud in the sky until you see a halo around the sun or moon.   Finally, Cumulonimbus clouds are those enormous, exciting thunderstorm clouds that can produce torrential rain, hail, lightning, and tornados.

You don’t need to watch clouds for very long before you realize there are one or two genera that you like especially well.   Most atmospheric scientists and weather enthusiasts will probably tell you that their favorite cloud genus is cumulonimbus because the huge impact these clouds can have on our lives makes them the most pertinent ones to study.  Although I do get pretty excited about cumulonimbus clouds, they are not my favorite sunset clouds.  Personally, I think that altocumulus and cirrocumulus are the most beautiful clouds (see pictures below).  Keep watching the sky this week to see if you can spot some of these cloud genera.