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The Formation Of Clouds

The world’s climate is controlled by the constant circulation of air masses, each having their own characteristics. Clouds form when two air masses of different temperatures collide, pushing the warmer air mass up.

As this hot air rises, the air can no longer hold this water vapour and it condenses forming the various types of clouds and shapes we see in the sky. For dry air, there is a temperature drop of 9.8 degrees Celsius for every km and for wet air there is a drop of 6.5 degrees Celsius for every km.

The point at which condensation occurs is the saturation point, which is the maximum amount of water vapour that the air can hold.

In order for the moisture in the clouds to condense and fall to the ground, the water molecules must combine and become heavy enough for gravity to pull them down towards the Earth.

Clouds can form anywhere in the troposphere and are light enough to be moved from one place to another by the wind. Most clouds can be classified by their shape and location and can be put into three distinct categories: cirrus, stratus and cumulus. These different clouds can combine to form variations of the three categories with new characteristics.

Cirrus Clouds

These are the highest forming clouds; at 18 000 feet and rising, they are thin, fibrous, white clouds that spread out across the sky. Often called “mares tails,” from the way they look, these clouds do not bring rain and instead are indicative of warm fronts approaching.

Since wind speeds at this altitude are much higher than the height at which other clouds are formed, we can watch the way cirrus clouds move across the sky to tell us which direction the changing weather will approach. This change in weather associated with cirrus clouds will take place within the next 24 hours. 

How To Identify Cirrus Clouds

Cirrus clouds are very easy to identify as they look like wispy, feathery clouds spread across the sky. When people think of clouds they often associate them with rain, but water droplets only form in clouds positioned at low altitudes.

Since cirrus clouds are found at higher altitudes, the freezing temperatures cause ice crystals to form. These crystals form as a result of distant storms that have thrown moisture up into higher altitudes

Cirrus Cloud Combinations

Most clouds can be grouped into the three main categories: cirrus, stratus and cumulus clouds.  These groups, however, can combine to form subcategories identified by different shapes.

If you are gazing up into the sky and see thin, milky sheet like clouds in the high altitude region, these are called cirrostratus clouds. Notice they combine the characteristics from both the cirrus and stratus groups. These clouds approach 12-24 hours before a rain or snowstorm.

Another combination forms cirrocumulus clouds, which appears as puffs, or ripples in the upper atmosphere. These are the least common clouds, often forming from the degeneration of cirrus or cirrostratus clouds. Usually seen during the winter months, these clouds indicate fair, but cold weather. Cirrocumulus clouds forming widespread layers or patches signify large, advancing, unstable air masses

Interesting Fact #2
When the “ceiling” appears to lower, the height of the cloud formations continue to get lower and lower eventually forming nimbostratus storm clouds. This effect is usually caused by an approaching warm front.
Stratus Clouds

Stratus clouds are flat, formless clouds that can occur at any altitude. They are gray and thick, and usually cover the entire sky. These clouds are formed when condensation occurs at the same level at which the air stops rising, and are responsible for our “overcast” days.

Identifying Stratus Clouds

Stratus clouds are one of the easiest clouds to identify and usually bring about periods of gentle precipitation. When scanning the sky, look for a flat, even cloud layer without any shape. They share the same appearance as fog; thick, but lifeless. In fact, fog is merely a very low-lying stratus cloud.

Combinations Of Stratus Clouds

Again we can see variations in precipitation and in cloud shape based upon the altitude at which the cloud is formed and whether it includes characteristics from other cloud categories.

Stratocumulus clouds indicate an approaching cold front and have the resemblance of whipped cream at heights of fewer than 6500 feet. Combining characteristics from both stratus clouds and cumulus clouds, stratocumulus clouds are mostly flat, with subtle cotton ball shaped puffs. These low-lying clouds cover the sky in dark, heavy masses and often form bands across the sky.

Precipitation usually occurs with blue-gray or whitish altostratus clouds. They vary in thickness based on their altitude (thinner at higher altitudes) and are formed by water and ice particles. These clouds usually gather at the head of heavy rain or snow storms.

Nimbostratus clouds are low, grayish, flat clouds that are associated with steady precipitation. These clouds are thick and dark gray in colour, forming continuous layers.  

Hints For Remembering Names

Stratus –layered or sheet like, low (50 - 6500 feet)

Cumulus – puffy cotton balls, vertical development

Nimbus – dark and rainy

Cirrus – feather-like, high (20 000 feet)

Alto – medium altitude (6500 - 20 000 feet)

Interesting Fact #1

“When a halo rings the moon or sun, rain’s approaching on the run”. This short rhyme actually proves to be an accurate weather prediction. The high altitude cirrus clouds comprised of ice crystals appear to form rings when they are located between the observer and the moon or sun.

Since cirrus clouds are usually followed by a wet warm front, this “halo” effect tells us that rain is approaching.

Cumulus Clouds

Cumulus clouds are formed when warm air rises and condenses, resulting in cloud shapes that look like cotton balls with flat bottoms. These clouds, for most of us as children, were the ones we used to lay back and imagine what shapes they were making.

Although most of these clouds are gentle, giant thunderstorms can form from these types of clouds reaching heights of 60 000 feet. Cumulus clouds, whether in the winter or summer, are signs of unstable warm air rising through the troposphere

Identifying Cumulus Clouds 

These clouds can be seen at any altitude and resemble puffy cotton balls. The danger comes when these puffy clouds build into huge, rising mounds. Watch for towering cumulus clouds in the distance, as they represent thunderstorms that are approaching.

These clouds are the leading edge of the thunderstorm and can generate high winds, hail and in some cases, tornadoes. Due to their nature, cumulus clouds are most often observed during the summer months.

Combinations Of Cumulus Clouds

Just like cirrus clouds, cumulus clouds can also share the characteristics of other cloud groups, as well as forming at various heights to produce different precipitations.

Cumulus clouds forming at what is considered a middle altitude of 6500 - 18 000 feet are called altocumulus clouds and are coupled with precipitation. Again, these clouds look like puffy cotton balls, elliptical in shape and grayish-white in colour.

Cumulonimbus clouds, like all nimbus clouds are associated with rain and build up vertically to look like a giant “anvil.” Hail, snow, dramatic wind shifts, lightning and tornadoes may also accompany these types of clouds.

These monstrous clouds bring thunderstorms and severe weather with them as they move through an area.

To gain a sense of direction for which way the storm is moving, you can look to the top of the clouds where wind shear cuts it off.  The anvil-shaped top usually points in the direction the storm is moving. These storms can indicate a cold front and may be preceded by a row of black storm clouds.

Interesting Fact #3
In Canada, weather changes generally come from the west. In order to spot an on-coming storm, you can scan the western part of the sky, but be aware that changes in wind direction can cause a shift in weather patterns.
How To Keep Safe In A Boat

When out on open water and a storm approaches, there are some general tips to follow to keep you and your family safe.

- Of course you should already be wearing your PFD!!!

  • Close all hatches and ports

  • Head for the nearest shore that is safe to approach

  • Point the boat at a 40-45 degree angle to the waves and steer into the wind

  • Secure any loose items to prevent them from being lost in rough water conditions

  • Constantly bail the boat if it begins to rain heavily

  • Change to a full tank of gas (if applicable)

  • Watch for other boats and debris

  • Unplug all electrical equipment and keep away from ungrounded metal objects if there is lighting

  • Keep everyone low and near the centre of the boat

Interesting Fact #4

If you bring a barometer with you, be sure to check it every few hours. Sudden drops in atmospheric pressure are indicators that a storm is approaching.

Dramatic changes in temperature also indicate wet weather to come, since the approaching cold front will push warmer, moist air upwards causing it to condense.