Weather Wise: Clouds

Hey everybody. Is it going to rain, or will it be a good day to grill out with the family? When you want to know what the weather is doing outside, the first place you probably look is up! Clouds can hint at a calm afternoon or an exciting evening of weather, and sometimes the clouds that look ominous aren’t really telling of severe weather at all. In this, the latest in a series of weather education blogs, you will learn more than you ever wanted to know about Clouds.

So lets start at the beginning. Where do clouds come from? The stories you were told as a kid are not true, like the one that goes something like this for example, “Clouds are made in a factory a far ways away and pumped out a smokestack…etc.” That is not how it works at all, and upon growing up, you probably made this discovery on your own. In fact, I found out that you couldn’t grab a piece of a cloud and put in in my pocket to take home after we booked a sight seeing flight in Myrtle Beach, back when I was 6. I reached out the plane window as we went through a cloud and tried to grab a piece, but my hand just got damp. It goes without saying that I was disappointed for the next 10 years or so. However, to this day you still aren’t sure exactly how it all works. You know that clouds are made up of some kind of water, and they get blown about by the wind. But why are they there? Why do some clouds grow into thunderstorms, while some make fun shapes that slightly resemble celebrities or animals? I’ll try my best to explain CLOUDS.

Cloud Factory by Marloag

-Your run of the mill Cloud Manufacturing Company. (Photo by Marloag)

It takes a bit of heavy lifting to get a cloud to rise. Moist air must be forced up somehow, whether it be from a front, warm or cold, or from some topographical feature, such as a tall hill or mountain. As that air gets forced upwards, it cools, and that water in it’s gaseous form (water vapor) condenses and forms water droplets. Warm air is capable of holding more water vapor than colder air, so any time air is cooled, it gets closer to being saturated, or reaching it’s saturation level. The point at which air becomes saturated is known as the dew point. I explained this in the Dew Point and Humidity posting a few weeks ago. Eventually, warm air rises high enough to the point in which it becomes saturated and droplets form. These droplets are smaller than rain drops or snowflakes. Once you get enough of the warm air to become saturated, a cloud becomes visible in the sky.

Instability, or when an air mass becomes unstable, describes an increased likelihood that a cloud will continue to grow and eventually precipitate. Obviously you have been told that warm air rises, and cold air sinks, so when you find yourself with an area of warmer air near the ground and colder air above it, voila! You have instability. That warmer moist air will want to rise high into the sky, forming a plethora of clouds.

Clouds come in many different shapes and sizes, and they even “reside” at different heights. The names of clouds are given by their appearance. The clouds that look similar to one another were created by the same process, whether it was by a cold front or an ocean breeze. Knowing how certain clouds formed is a grassroots method of forecasting. A British man by the name of Luke Howard devised the system of cloud classification nearly 200 years ago that we still use to this day. Once you get a grasp of the names, it becomes easier to understand. Unfortunately, Latin was popular in that day and age, so all of the classifications are in that language. Just remember the following… there are 3 main types of clouds, cotton balls, feathers and bed sheets. Also, let it be known that there are generally 3 heights that clouds float around in, high, somewhere in the middle, or low to the ground. These 6 categories all come with a Latin prefix or suffix except for the lowest ones, which have no prefix. To learn more about English, and what a prefix and suffix are, please see some other blog.  Alto means “middle” and describes those clouds riding along high in the sky, but not too high. Cirro in latin means “a curl of hair.” You might ask, well what does this have to do with clouds? Well, Cirro is used to describe the highest clouds in the atmosphere, made up of mostly ice crystals. They are generally wispy in nature and if you use your imagination, they slightly resemble wavy hair. Now onto the suffixes… Generally any cloud that has a uniform, sheet like appearance is known as a Stratus cloud. You can have them at a low level, known as stratus, or a mid level, known as altostratus, or a high level, which we call cirrostratus. Now you can see that cloud descriptions aren’t that complicated after all. The cotton ball or generally fluffy clouds are called Cumulus, which means “heap” in Latin. Again, you can find this particular type of cloud in all three height levels. The last classification is not actually a different type of cloud, but if the particular cloud you are looking at is precipitating, if then gets the suffix Nimbus, which by no surprise means “rain.” At any time, you can have different clouds in all three layers occurring at the same time and this is common.

-This will help explain things more visually. (Diagram-UCAR)

Nearly 4 miles up in the atmosphere, the air temperature is too cold for moisture to retain it’s liquid state. Tiny ice crystals form the clouds instead. This can make the appearance of these cirrus clouds very different than their lower counterparts. They appear to be semi-transparent and every once and a while if the angle is right, you might be able to make out a sun dog caused by the visible light from the sun being split into the visible spectrum, aka a rainbow, but one not caused by rain. These clouds generally mean fair weather, however sometimes they can indicate the arrival of bad weather. Generally the “bad weather” cirrus clouds are called “mares’ tails.” They are just feathery cirrus clouds with one end rolled up.

-"Mackerel scales and mare’s tails, make lofty ships carry low sails."

Cirrocumulus clouds are very high, fluffy clouds. Sometimes they can appear to look like fish scales, or “mackerel skies.” These clouds are formed when wind shear is taking place in the atmosphere. Wind shear is a component of severe weather, so when these clouds are seen, sometimes there might be bad weather on the way.  This is the second component to the folklore I placed in the caption above.  Basically all it is saying is that the combination of mares’ tails and the mackerel skies is a good indication of bad weather on the horizon, so ships will then take down their sails to not capsize.

Cirrostratus clouds, the last form of high level cloud, is a transparent sheet of ice crystals similar to a silky wedding veil. Sometimes this thin layer will thicken. This can be the signal of an approaching warm front, which could bring precipitation to an area within the next half a day to 24 hours. Eventually the cirrostratus clouds will get replaced by lower and lower clouds.

-Note that the sun is hidden behind a high layer of cirrostratus clouds.

Somewhere in the middle, or 1.5 miles and 26,000 feet, you’ll find the middle layers of clouds with the alto prefix. The water droplets that make up these clouds are “supercooled,” meaning that they are able to remain in the liquid state since they are made of pure water and their size is very small. This sets them apart from their wispy neighbors above them.

Altocumulus clouds are white and gray puffs, sometimes forming waves and streets (or cloud bands.) They do not have a wispy appearance and the borders are well defined. These are generally fair weather clouds that rarely precipitate. However, they do indicate an area of unstable air aloft. This particular type of cloud forms with lift which could signal the near arrival of a cold front. (If they appear on a summer morning on a hot and humid day, the atmosphere is probably ripe for afternoon thunderstorms.)

-Altocumulus clouds forming rows, or streets.

Altostratus clouds are the other mid-level cloud other than altocumulus. These clouds are a mix of ice and liquid water and are generally a light grey on an otherwise sunny day. They are much thicker than their cirrostratus cousins, and let less light through. Generally the thicker the cloud, the darker it gets since less light is able to pass through. Altostratus clouds indicate the arrival of widespread precipitation.

-Altostratus clouds at sunset.

-Altostratus clouds at sunset.

Finally we have reached the group of clouds found closest to the ground. Stratus clouds generally have a dark, flat base. If they are precipitating, you can throw the nimbus suffix on the end. If you have ever tried to drive through fog, you are actually driving through a stratus cloud that is reaching the ground.

-A stratus cloud attempting to swallow a bridge.

Cumulus clouds are your basic, low level, fair weather clouds. They can take on various shapes, but for the most part, they appear to be a fluffy, oversize cotton ball. Don’t let the fluffy appearance fool you however… these clouds way tons, literally. The average cumulus cloud is 1 cubic kilometer, with air density of 1.007 kg/m3. The density of the water in the cloud is roughly  1.003 kg/m3. That is why the cloud is able to “float” in the air. Using a fancy equation, one is able to calculate the the cloud contains nearly 1,000,000 cubic meters of water droplets, weighing roughly… a lot. Anywhere from hundreds of thousands to millions and even billions of pounds depending on the cloud. So if they decide one day that they don’t want to float anymore, we will all be crushed.  Of course, I don’t see this day ever coming.

-They're all just up there floating around innocently now, waiting for the perfect time to strike.

Some clouds have a low base but extend extremely high into the atmosphere. These can be described as “vertical” clouds, or those that are taller than they are wide. A good example of a vertical cloud is the Cumulonimbus. These are your thunderstorm clouds, and the bricks and mortar of any supercell or hurricane.  A supercell thunderstorm can reach heights of 60,000 feet or more. That is over 10 miles high! Airplanes normally fly at around 30,000 to 40,000 feet, so you usually have to divert around these monsters. These are heavy rain and hail producers, and on some occasions they can even spur tornadoes. If you find cumulonimbus clouds on the open seas between the months of June and November, they might even grow into a hurricane.

Hopefully you have learned a thing or two about all types of clouds, from high to low and fair weather and bad weather. As always, if you have any questions, comments, complaints or suggestions, email them to me at Brad@SWATChasers.com. Some people are weather wise, some people are otherwise. Don’t be the latter.

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