How to predict the weather with clouds

On a warm evening in 1802, upstairs from a laboratory at 2 Plough Court in London, 30-year-old Luke Howard, a chemist and amateur meteorologist, rose before the Askesian Society—a jovial
group of scientists whose irreverence was only matched by their affinity to inhale laughing gas for amusement—and presented his essay called On the Modification of Clouds, where the Latin terms “stratus,” “cirrus,” and “cumulus” were first used.

With this, Howard became known as the father of clouds, and although the connection between clouds and the weather had been around for thousands of years, finally there was a universal naming system and, most importantly, it was in Latin. Today, the plaque on Howard’s house reads: “The Namer of clouds lived and died here.”
For modern human beings, checking tomorrow’s weather is as easy a clicking an app on their phones or watching the evening news, but spend any amount of time high in the mountains and out of reach of modern methods of communications that we take for granted, and you’ll soon discover that the weather can change dramatically in a matter of hours, if not minutes. Sunny one moment, gale-force rains the next.

Being prepared for any situation is all about reading the signs that hint at what the future holds, and when it comes to weather, the future is in the clouds. Essentially, meteorology is the study of the air’s effect on the environment and the various natural elements that affect the air—temperature, humidity, wind, and pressure.

These elements, since the dawn of civilized man, have exerted a profound influence on the habitability and civilization of the very planet. To a professional meteorologist, the observation of the types of clouds and the forms of precipitation are one of the most important readings they can observe, so it stands to good reason that even a casual observer—especially one in a survival situation—would gain from knowing the physical process of the atmosphere.

Predicting the weather

It isn’t too difficult to predict the weather if you’re in familiar territory. Near your home base, the weather today will probably be similar to what it was yesterday. But remove yourself from your familiar territory and the weather will be as foreign as if it were another planet. It is important to understand the movement and formation of the clouds as a clear signal to decide whether you’ll be building a shelter out of branches and leaves or an ark out of logs and mud.

Classification of clouds

From the ground, clouds can be divided into four main groups based on their structure and location: cirrus, alto, stratus, and cumulus. These basic forms may be present simultaneously, evolve from one form to another, and combine into various permutations, but elevation is a predominate factor in classifying clouds: Cirrus clouds occur only in the upper part of the troposphere, while stratus occur only at the lower levels. However, the tops of cumulus clouds may thrust up to the levels of cirrus territory, while the bases are only a few hundred feet off of the ground.

High-level clouds

  • Cirrus: From the Latin meaning a curling lock of hair, these are the highest forming clouds in the sky. Their main characteristics are that they consist of fine ice crystals and that they have a fibrous structure and wispy streaks in appearance. Sometimes referred to “mare’s tails,” they drift rapidly across the sky on high-altitude winds. As these feathery clouds spread across the sky, it usually indicates that fair weather is upon you. These clouds rarely gather together, but a gradual increase of cirrus cover indicates that a warm front is moving in. Because cirrus clouds are quick moving, use them to find out from which direction. Cirrus clouds indicate a change in the weather, usually within a day.
  • Cirrostratus: Cirrus, meaning curled hair, and stratus, meaning layered, a cirrostratus is a very thin high-altitude cloud that uniformly covers the sky in layers like a light gray veil. These clouds will usually give the sky a uniformly milky appearance or sometimes a slightly fibrous, like a thin, tangled web. When these light, pale veil clouds blanket across the sky, rain is on its way within a day or so.
  • Cirrocumulus: These clouds are named from a combination of cirrus (wisps of curled hair) and cumulus, meaning heap. These clouds are a larger collection of layered cirrus clouds forming light heaps, which have been described resembling white flakes of lamb’s wool or the scales of a fish (specifically a mackerel) across the sky. When old folks look at the clouds and remark, “Mackerel sky, storm is nigh,” they are looking at cirrocumulus clouds. Although a rainstorm usually isn’t “nigh,” it indicates a cold front for most of the country and a hurricane in tropical regions.

Medium-level clouds

  • Altocumulus: Meaning middle-layer heaps, these differ from cirrocumulus in that the bundles of clouds are larger, more defined, and arranged in banks. It will appear as though a fleece blanket has been pulled across the sky. Not to be confused with the “mackerel sky” appearance of the cirrocumulus, the altocumulus is at a lower altitude and has larger bundles. Warm, humid and sticky days will produce altocumulus and thunder-storms will likely be present by the afternoon or evening.Altocumulus.jpg
  • Altostratus: Meaning middle-altitude layers, altostratus clouds are dense sheets of gray or bluish clouds showing a fibrous structure. Though the sun can be discerned through them, they are darker than cirrostratus and can block out the sun.

Low-level clouds

  • Stratocumulus: Formed by air turbulence, these are a low cloud layer consisting of large lumpy masses of a dull grey color. They are often in patterns (like rolls with blue sky in between) and resemble altocumulus, but are lower. Rain rarely occurs with these types of clouds, and if the temperature between the day/night’s high and low is only a few degrees, stratocumulus point to dry weather.
  • Stratus: This is a low, evenly grey layer of fog-like cloud that comes close, but doesn’t touch, the ground. It produces a fine mist and is greatly affected by local air currents. Since they cover the entire sky usually in what is normally described as “overcast,” the humidity level is up high enough to produce drizzle at most. Normally in the morning and burning off by afternoon, stratus clouds can start as fog (if they touch the ground).Stratus-Opacus-Uniformis.jpg

Large vertical clouds

  • Cumulus: Latin for “heap,” cumulus clouds are high-piled clouds with flat bases and domed tops that can resemble tall towers. Often resembling cauliflower in shape, there are two basic types: Cumulus humilis (fair-weather cumulus) are flat cumulus clouds; cumulus congestus are much greater in size but are usually taller than they are wide. They often develop into cumulonimbus. Most cumulus are fair-weather clouds and are produced generally in dry conditions of a fair summer (or hot) day. They only last for a short time, but if they do generate rain, it will be light. However, enough cumulus clouds can grow into a cumulonimbus formation and produce thunderstorms.
  • Cumulonimbus: These are what we call thunderclouds or shower clouds, great masses of clouds rising like mountains that dominate the sky. They often have an anvil shape at the top and bring thunderstorms, heavy rain, squalls, and hail. Make no mistake when you see these clouds. They’re enormously tall and can forecast some extreme weather, from heavy rain, snow, thunderstorms to tornadoes and hurricanes. When you see large masses of cumulonimbus on the eastern horizon (the anvil shape points in the direction of travel) prepare yourself for rain or worse.
  • Nimbostratus: Dense, shapeless, and ragged, nimbostratus are a low layer of dark clouds that blanket the sky. Nimbostratus are often connected to altostratus above it, and almost always deliver rain. You can readily assure yourself that rain (or snow in cold climates) is coming and lots of itNimbostratus clouds in Istanbul.jpg

Why Does It Rain?

It is common to see a cloud exist for a couple of days without releasing any rain, but on other occasions, a heavy downpour will seem like it came out of nowhere. Water droplets in clouds form via
two processes that might lead to rain: ice crystal and capture.

  • Ice Crystal: When air rises, it cools by expansion and as it cools, relative humidity increases. When the air reaches saturation (of moisture), cloud droplets form.
  • Capture: As clouds rise high into the sky, they allow some moisture to escape and as it falls, it collides with other water droplets to create larger droplets in a cloud that is not a rain cloud. There are a variety of methods that lead to rainfall, but the most common is coalescence, where tiny water droplets fuse with each other to form larger and larger droplets until their weight is greater than the force of air resistance that keeps them aloft.

Depending on temperature and altitude of the cloud, water droplets can be as large as 5 mm in diameter when they fall. A large raindrop like this will reach a terminal velocity of around 20 mph when it hits the ground.

Flash Floods

Flash flooding is a major killer; what looks like a little bit of moving water can have a serious undertow that can easily sweep you or your car away. Because most storms occur at night, flash floods are also frequently at night, which makes them more difficult to see.

  • Do not attempt to drive or walk across a flooded roadway or low water crossing. Nearly half of all flash flood deaths are vehicle-related. Moving water 2-feet deep can carry away most cars.
  • If your vehicle becomes caught in high water and stalls, leave it immediately and seek higher ground if you can do so safely. Rapidly rising water may sweep a vehicle and its occupants away.
  • When the threat of a flash flood is evident (a dry season followed by the first heavy rain), be aware of your location and head to higher ground. If water looks like it has been there before (e.g. dried creek bed, collected drift logs), a flash flood will likely choose the same course again.

The Life of a Thunderstorm

Thunderstorms are one of Mother Nature’s most impressive displays, as there are a multitude of natural phenomena occurring simultaneously and in concert to produce a thunderstorm. Depending on the type and number of cells, thunderstorms may be divided into four main categories:

  1. Single-cell storms are generally weak, short-lived, and loosely organized. They blow out as quickly as they blow in and typically don’t produce a lot of rainfall.
  2. Multi-cell cluster storms are the most common type of storm and consist of a series of cells moving along as one unit, usually rotating slowly between each other.
  3. Multi-cell line storms, commonly called “squall lines,” consist of a long line of storms with a continuous wind front at the leading edge. These produce a lot of rain over a wide territory.
  4. Super-cell storms have a single updraft, are very strong, and always produce significant severe weather. However, all thunderstorms, regardless of their size, length, or severity, go through a three-stage life cycle.

Development Stage: The first stage occurs when the thunderstorm begins to develop. At this infant stage, the storm is only a series of upward-moving air currents that can reach a height of around 20,000 feet, nearly the zone of high-based altocumulus clouds. As moisture becomes more plentiful in the lower atmosphere, the base of the storm may extend downward toward the ground.

Maturation Stage: This is the strongest and most dangerous stage of the storm’s life cycle. At this stage, the storm contains both upward and downward moving air currents (updrafts and downdrafts). The downdraft regions supply rain to the area and causes cooling from the high-altitude air being pushed toward the ground. When the cool downdraft hits the ground, it spreads out and forms winds called a downburst. At the top of the storm, the updraft rapidly decelerates and clouds spread out and form an anvil. If the updraft is particularly strong, however, an “overshooting top” will form above the anvil. Underneath this area are usually severe weather conditions relative to the rest of the storm.

Dissipation Stage: Eventually, excessive rainfall and downdraft will combat and weaken the updraft. The wind front will move away from the center of the storm and sever its own supply of energy (updraft provides moisture for rainfall). Air pressure will self-regulate and the storm will end.

Story by Ryan Lee Price |

Editors Note: A version of this article first appeared in the December 2014 print issue of American Survival Guide.