Appearance:
1. It is a gray cloud layer with a uniform base.
2. It often covers the sky and gives a dull and
overcast look.
3. It is thick enough to obscure the sun, but a
thinner layer creates a diffuse glow.
4. Sometimes it appears as a ragged sheet and
when the sunlight is visible through this cloud, its
outline is clearly noticeable.
Formation:
Large warm moist air lifted upward and cooled
down.
Weather indicator:
1. This cloud can produce drizzle, light rain or
snow.
2. This cloud creates fog close to the ground.
These low level clouds are found below 2 km
above the ground in the troposphere. This is a
combination cloud of stratus and cumulus. These
types of clouds are called twain clouds. These
clouds are also called cumulostratus (cumulus
means heap and strato- means layer). We can
understand from its name that this is a large cloud.
Appearance:
1. It is a large dark, rounded mass or rolled cloud.
It is lumpy and looks like a honeycomb.
2. It can be gray or patchy white.
3. It is a very thick cloud but can still produce
dappled light from the sun.
Formation:
Warm moist air lifts. The water droplet cooled at
the high altitude and formed this cloud.
Weather indicator:
This cloud generally doesn't produce rain but if they
do, they only produce light rain. It rarely indicates
storms in the form of lightning and gusty wind.
Cumulus means heap or pile and nimbus means
cloud in Latin. This is a large cloud and can
normally reach an altitude of 12 km. But the top
of this cloud can reach its extreme height at
20-21 km. This type of cloud falls into all
categories from low to high level clouds.
Appearance:
1. This is a heavy and dense cloud and forms
a vertically tower-like shape.
2. The top of this cloud is flat or anvil-shaped.
Formation:
Warm moist air uplifts rapidly. Then it condensed
and built upward carried by powerful unstable air
current.
Weather indicator:
Cumulonimbus clouds are associated with extreme
weather conditions, like heavy rain, thunderstorms,
hail, tornadoes, etc.
Mid Level Clouds
The mid level clouds are found at an altitude of
2-8 km. There are basic three types of mid level
clouds and they are altocumulus (Ac), altostratus (As),
nimbostratus (Ns).
Alto/altum means high and cumulus means heap in
Latin. These mid level clouds are large and found at
an altitude of 2-7 km.
Appearance:
1. It is a white/gray cloud, often appearing with a
layered mass or roll pattern.
2. It is the most common cloud. It covers the entire
sky with its patches and often appears with the other
clouds.
3. When this cloud passes in front of the sun or moon,
a corona appears with a red colour outside and blue
colour inside.
Formation:
Moist air rises and cools at high altitudes. When the
temperature reaches the dew point, the water droplets
cool and form the cloud.
Weather indicator:
Altocumulus isn't associated with severe weather
conditions, but sometimes it indicates the change
in weather. The towering altocumulus is a signal of
thunderstorms later in the day.
Altum means high and stratus means flat or spread
out in Latin. These mid level clouds are featureless
and found at an altitude of 2-7 km.
Appearance:
1. These clouds are uniformly spread over the sky
with a bluish-gray tint.
2. They can be striated or fibrous in appearance and
can fully or partially cover the sky.
3. Like other cumulus clouds, altocumulus doesn't
grow vertically but remains flat.
4. The sun or moon can be visible through these
clouds but as if looked through faint glasses.
Nimbus means cloud or halo and stratus means.
It forms in the middle altitude but gradually
spreads vertically to the low and high altitudes.
Thus it is called a multi level cloud. The important
features of this cloud are given below.
Formation:
Large warm moist air uplifts to the middle
troposphere. When the temperature reaches below
the dew point, the moisture condenses into tiny
water droplets and leads to the cloud formation.
Weather indicator:
This cloud doesn't indicate any significant rain
but often predicts the arrival of a warm front
(edge of warm air) followed by drizzle or light rain
or snow.
High Level Clouds
High level clouds are found at an altitude above
6 km. The common high level clouds are cirrus (Ci),
cirrocumulus (Cc), cirrostratus (Cs).
The Latin of cirrus means curl or fringe. These
clouds are found at a height of 6-20 km above sea
level. The important features of these clouds are
given below.
Appearance
1. These clouds are detached, white fibrous, and
wispy.
2. They are white colour but at dusk, they can be
seen as light gray. Before sunrise and sunset, they
look yellow or red.
3. They generally do not diminish the brightness of
the sun.
Formation
The warm dry air moves upward. At the higher altitude,
the water droplets deposited onto the dust particles in
the air. The water droplets freeze at the freezing point.
Therefore these clouds are made of ice crystals.
Weather indication
These clouds indicate the change in the weather and
thunder or storm is on the way.
It is a high altitude cloud and can appear at an altitude
of 5-12 km. The features of this cloud are given below.
Appearance
1. These clouds are made of supercooled small water
droplets.
2. They appear as white patchy sheets or small cotton
balls or grains arranged in a regular pattern. They have
a ripple structure.
Formation
Moist air rises to the upper atmosphere. At the dew
point the water droplets cool and form ice crystals.
Thus the cloud forms.
Weather indicator
Cirrocumulus indicates fair weather. But if they are
seen with other types of clouds like cirrus or
cirrostratus, can precede a significant weather change.
Cirrostratus is a high altitude cloud and can appear at
an altitude of 6-13 km. The important features of
cirrostratus are given below.
Appearance
1. It is translucent, white, thin, uniform, and a fibrous
cloud.
2. Sometimes they are difficult to detect and form halos
around the sun or moon.
3. These clouds are not thick enough to prevent the
shadows of objects on the ground.
Formation
These clouds are made up of ice crystals formed by
the condensation of moist air at high altitudes.
Weather indication
These clouds indicate heavy moisture in the higher
troposphere. But they don't produce precipitation.
They sometimes indicate a warm front (edge of
warm air) and rain or snow may occur in 12-24 hours.
What is Weather Front?
The air of the atmosphere is flowing across the
planet. The temperature, density, and humidity of
the air are different in different places. The
boundary between two different air masses (with
different temperatures, densities and humidities)
is called a weather front.
What is a Cold Front?
When a cold-dry air mass pushes into the warm-
humid air mass, there is a cold front. As the cold
air advances, it pushes the warm-humid air quickly
with a steep slope upwards. Thus, the clouds form,
temperature drops and we can see severe weather
like storms, gusty winds, thunder, and heavy rain.
In the weather map, it shows a blue line with triangles
pointing toward the movements.
What is a Warm Front?
If the warm-humid air mass pushes into the cold-dry
air mass, we can see the warm front. Because the
cold air is denser, the warm air is pushed up but with
a less steep slope. White clouds and little precipitation
can be seen there. As the warm air moves further
upwards to the slope, the mid level clouds are seen
ahead of the active weather like a rise in temperature
along with steady precipitation. The cirrus cloud is one
example of a warm front. In the weather map, it shows
a red line with semicircles pointing toward the direction
of the movements.
What is a Stationary Front?
When the cold and warm air masses meet. But neither
the air masses try to replace each other, we get the
stationary front. In the stationary front we get the same
kind of weather associated with the warm front, but it
lasts longer. So, we can see a prolonged cloudy sky, rain,
etc for several days. The stationary front is shown as
alternating blue triangles and red semicircles in the
weather map.
What is a Occluded Front?
When the cold and warm air masses push each other,
the fast moving cold front overtakes the slower moving
warm front. As the two fronts meet, the warm air is
pushed up. But the cold denser air behind the cold front
also moves forward and pushes the warm front above the
ground. Thus, we get an occluded front. In the occluded
front we get active weather and sometimes it leads to a
severe weather condition.
How does Hail and Sleet form?
Hail: In the summer season the thunderstorm updrafts.
At an altitude when the temperature is at the dew point,
the water vapour of the cloud transforms into water
droplets. The water droplets move to the top part of
the cloud. At the top part, the temperature is very low,
and the droplets combined with the dust particles
become a tiny hail. The hail then moves down at the
bottom of the cloud and waits for another updraft. If
the cloud moves upward again, the tiny hail moves
at the top of the cloud and freezes with the contact of
the ice crystals. Then they become hailstones. Due to
their weight and gravity, the hails fall down on the
ground.
Sleet: When a layer of warm air is sandwiched
between layers of cold air, the moisture of the cloud
changes its state from ice to water and then water
to ice again. Therefore the sleets form and come to the
ground.
How does the Freezing Rain and Snow
form?
Freezing Rain: The freezing rain forms the same as
the sleet, but it is more dangerous. In winter when the
snow comes in contact with the warm air, it melts and
falls as rain drops. But it freezes immediately when it
comes in contact with the freezing temperature of the
ground. Ice forms on the road, sidewalks, and the
cycle track. People have to be very careful to move
on these slippery icy paths.
Snow: The water droplets transform into ice crystals
at a very high altitude. If there is no warm layer of air,
the precipitation falls in the form of snow.
What is Lightning?
When moisture air is uplifted to an altitude, the water
vapour transforms into the water droplets at the dew
point. And the cloud is formed. If the clouds still move
upwards, at higher altitudes it consists of sleets and
ice crystals. The ice crystals have a positive charge
(+ve) and the sleets have a negative charge (-ve).
The positively charged ice crystals move upwards
and accumulate at the upper part of the cloud but
the negatively charged sleets stay at the bottom part
of the cloud. Due to the negative charge of the sleet,
the positive charge is induced near the ground. As
the opposite charges attract, the negative charge
from the cloud moves toward the positive charge
near the ground. When the two opposite charges
(positive and negative) collide, electricity is produced
and we see a flash of light. It is lightning.
