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You can learn how observing the clouds can help in making short range, local weather forecasts.

Introduction | Wind Vanes | Barometers | Hygrometers | Anemometers | Nephoscopes Rain Gauge | Snow Gauge | TV Weather | Charting | Forecasting | Cloud In A Jar

Snow Water | Weather Station | Storm Tracking | Rain In A Jar | Frost In A Can

Clouds

• Barometric Pressure
• Humidity
• Temperature
• Winds
• Charting
• Worksheet
• Psychrometrics

Cumulus:  Cumulus clouds are the puffy clouds that look like balls of cotton. Cumulus clouds that do not get very tall are indicators of fair weather. If they begin towering, thunderstorms may occur. The bottoms of cumulus clouds are relatively close to the ground.

Cirrus:  Cirrus clouds are high feathery clouds. They are up so high they are actually made up of ice particles. They are indicators of fair weather when they are scattered in a clear blue sky.

Stratus:  Stratus clouds look like flat sheets of clouds. These clouds can mean an overcast day or steady rain. They may stay in one place for several days.

Nimbus is another word associated with clouds. Adding "nimbus" means precipitation is falling from the cloud.

 

Cumulonimbus clouds are the "thunderheads" that can be seen on a warm summer day and can bring strong winds, hail, and rain.

 

Nimbostratus clouds will bring a long steady rain.

Clouds are possibly the most interesting of all weather phenomena. While there are a wide variety of cloud shapes and sizes, they are all made of the same thing: condensed water or ice. Clouds form when rising air, through expansion, cools to the point where some of the water vapor molecules "clump together" faster than they are torn apart by their thermal energy. Some of that water vapor condenses to form visible cloud droplets or ice crystals.

 

There are three basic cloud types:

Convective Clouds:  Convective clouds are those which are produced through solar heating of the Earth’s surface. This creates bubbles of warmer air which are more buoyant than the atmosphere around them. These bubbles ascend, expand and cool, causing water vapor to condense and become visible as a cloud.

 

These types of clouds are most often detached clouds, generally dense and with sharp outlines, developing vertically in the form of rising mounds, domes or towers, having their bases located in the lower parts of the atmosphere.

Mackerel Sky:  The distinctive sky covered with many small cirrocumulus or altocumulus clouds, resembling the markings found on a mackerel. It is also called a “buttermilk sky” and is considered to portend good weather.  One folk proverb maintains:

 

Mackerel sky, twelve hours dry!

Thunderheads:  The distinctive towering clouds that accompany thunderstorms. Although several storm cells can develop, each individual cell lasts about 30-60 minutes and has three stages:  Cumulus stage:

 

·          Starts with a warm plume of rising air.

·          The updraft velocity increases with height.

·          Entrainment pulls outside air into the cloud.

·          Supercooled water droplets are carried far above freezing level and cloud begins to tower.

Cumulus Stage

Mature Stage—Height in feet

Mature Stage:  A downdraft is initiated by frictional drag of the raindrops. The slight lean to the tower at this stage keeps precipitation and downdraft from interfering with the updraft.

 

·          The heaviest rains occur.

·          Evaporative cooling leads to negative buoyancy.

·          The top of the cloud forms an anvil top.

Dissipating Stage: 

 

·          The downdraft takes over entire cloud.

·          The storm deprives itself of saturated updraft air.

·          Precipitation decreases.

·          The cloud evaporates.

To find the height of convective type clouds:  Temperature (in °Fahrenheit) minus dewpoint temperature (in °Fahrenheit). Multiply this number by 220. This will give the approximate height of the clouds in feet.

 

Stratiform Clouds:  If air masses only rise a short distance over a large geographical area after reaching dewpoint, layer clouds (such as stratus) will form. Stratiform clouds typically cover much larger areas and are caused by much broader layers of more slowly rising air. Stratiform clouds have a more uniform, featureless appearance, and often cover the whole sky. It is these types of clouds that produce steady, long continued rains and snows.

 

Fog:  A fog is simply a cloud on the ground. It is conventionally defined as occurring when the visibility is 1000 meters (3,281 feet) or less. Since the air is usually stable when a fog occurs, the cloud is a stratus cloud, and sometimes the base of the fog may lift, producing a low stratus formation. Two things are necessary for a fog: saturation and calm wind conditions. Saturation can be produced by the addition of additional water vapor, or by cooling to the dewpoint. Haze is considered to be a lesser form of fog and may appear, affecting the visibility in the air before fog actually forms.