Cloud Formation Cloud Formation

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Regional Gliding School

Cloud Formation Cloud Formation

Clouds form when invisible water vapour that is present in the air changes into its visible

form as water droplets or ice crystals, via condensation or sublimation. This occurs when:

• the relative humidity is high,

• when condensation nuclei are present, and

• when there is a cooling of air.

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Lifting Agents Lifting Agents



Orographic lift Orographic lift

Air blowing against a range of hills or mountains is forced Air blowing against a range of hills or mountains is forced upward into a region of lower pressure, expands and cools.

upward into a region of lower pressure, expands and cools.

Condensation will occur when the dew point is reached.



Frontal lift Frontal lift

A mass of warm air is forced aloft and rises over the cold air. A mass of warm air is forced aloft and rises over the cold air.

The rising warm air cools by expansion and clouds are formed.



Convection Convection

As the sun heats the earth unevenly, rising currents will occur. As the sun heats the earth unevenly, rising currents will occur.

This is convection. The rising air expands and cools. This This is convection. The rising air expands and cools. This

produces condensation and cumuliform cloud forms at the top of produces condensation and cumuliform cloud forms at the top of the column of air. Further ascent and cooling causes rain.

the column of air. Further ascent and cooling causes rain.

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Lifting Agents Lifting Agents



Convergence - Convergence -

 Air is forced into a region, as at the center of a low, Air is forced into a region, as at the center of a low,

convergence is occurring. The excess air is forced to rise, convergence is occurring. The excess air is forced to rise,

as it rises it expands and cools. When the condensation as it rises it expands and cools. When the condensation

level is reached, cloud form.



Turbulence Turbulence

 As wind blows over an uneven or rough surface or when As wind blows over an uneven or rough surface or when uneven heating occurs, vertical currents are created. Air in uneven heating occurs, vertical currents are created. Air in

the upward motion cools by expansion and if enough the upward motion cools by expansion and if enough

moisture is there condensation occurs. This results in moisture is there condensation occurs. This results in

cumulus cloud.

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Precipitation Precipitation

When water droplets (visible When water droplets (visible as a cloud) grow sufficiently in as a cloud) grow sufficiently in

size and weight to fall due to size and weight to fall due to

gravity.

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Forms of Precipitation Forms of Precipitation

 Drizzle, rain, freezing drizzle, freezing rain Drizzle, rain, freezing drizzle, freezing rain

 Hail, snow pellets (soft hail) Hail, snow pellets (soft hail)

 Snow Snow

 Ice prisms Ice prisms

 Ice pellets Ice pellets

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Drizzle, freezing drizzle, snow Snow or rain (continuous)

Ice pellets (continuous) Hail, ice pellet showers Snow shower, rain showers

Snow or rain (intermittent)

Ice prisms

PRECIPITATION CLOUD TYPE

Stratus and stratocumulus

Thick altostratus and nimbostratus Thick altostratus and stratocumulus

Altocumulus, heavy cumulus, cumulonimbus

Cumulonimbus

Any rain cloud (below freezing) No clouds necessary

Snow pellets Heavy cumulus

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Confirmation Stage Confirmation Stage

NOTE: You must use the buttons in the Confirmation Stage

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A B C D

Orographic Lift Frontal Lift

Let's try a few review questions on Meteorology:

Question #1 -

A mass of warm air is forced aloft and rises over the cold air. The rising warm air cools by expansion and clouds are formed. This phenomena is known as .

Convection Convergence

Meteorology Meteorology

Clouds, Precipitation & Fog Clouds, Precipitation & Fog

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Lifting Agents Lifting Agents



 OrographicOrographic lift lift



Air blowing against a range of hills or mountains is forcedAir blowing against a range of hills or mountains is forced upward into a region of lower pressure, expands and cools.

upward into a region of lower pressure, expands and cools.

Condensation will occur when the dew point is reached.



 Frontal liftFrontal lift



A mass of warm air is forced aloft and rises over the cold air.A mass of warm air is forced aloft and rises over the cold air.

The rising warm air cools by expansion and clouds are The rising warm air cools by expansion and clouds are formed.

formed.



 ConvectionConvection



As the sun heats the earth unevenly, rising currents willAs the sun heats the earth unevenly, rising currents will occur. This is convection. The rising air expands and cools.

occur. This is convection. The rising air expands and cools.

This produces condensation and cumuliform cloud forms at This produces condensation and cumuliform cloud forms at the top of the column of air. Further ascent and cooling the top of the column of air. Further ascent and cooling causes rain.

causes rain.

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A B C D

Stratocumulus Stratus

Question #2 -

What cloud will produce continuous rain?

Nimbostratus Cirrostratus

Meteorology Meteorology

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Drizzle, freezing drizzle, snow Snow or rain (continuous)

Ice pellets (continuous) Hail, ice pellet showers Snow shower, rain showers

Snow or rain (intermittent)

Ice prisms

PRECIPITATION CLOUD TYPE

Stratus and stratocumulus Thick altostratus and nimbostratus Thick altostratus and stratocumulus

Altocumulus, heavy cumulus, cumulonimbus

Cumulonimbus Any rain cloud (below freezing)

No clouds necessary

Snow pellets Heavy cumulus

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Fog is a cloud, usually stratus, in contact with the ground. It forms

when the air is cooled below its dew point, or when the dew point is

raised to the air temperature

through the addition of water

vapour.

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

clear skies clear skies



moist air moist air



light winds (2-5 knots) light winds (2-5 knots)

Usually forms on clear nights. Conditions that favor the formation of radiation fog are:

The ground cools losing heat through radiation. The air in direct contact with the earth’s surface is cooled. If this air is

moist and the temperature is lowered to the dew point , fog will

form.

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Forms when warm moist air

moves over a cold surface.

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scan scan Advection Advection Fog Fog

WARM MOIST AIR

9

COLD

LABRADOR

CURRENT

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10

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Caused by the cooling of air

due to expansion as it moves up a slope. A light upslope wind is

necessary.

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scan scan

example of example of upslope fog upslope fog

MSL ^YQR

Regina

YBR

Brandon

YPG

Portage La Prairie

YWG

Winnipeg

Stable, moist easterly flow

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Forms when cold air passes over a warm water surface. Evaporation of the water into the cold air occurs until the air becomes saturated. The excess water

vapour condenses as fog.

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Often found near fronts. Warm front fogs are the most extensive and are caused by the cold air becoming saturated by

evaporation from rain falling from the warm air. It is also known as precipitation-

induced fog.

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FRONTAL FOG FRONTAL FOG

SATURATION OF COLD AIR BY

EVAPORATION OF FALLING PRECIPITATION

FOG

NS NS

ST ST

32

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Caused by the addition of moisture to

the air through evaporation of precipitation.

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At very low temperatures, the air may become full of ice crystals. The ice

crystals, which formed by sublimation, may suddenly appear when an aircraft engine has been started (the exhaust contains water

vapour, condensation nuclei and the engine

create mixing).

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Confirmation Stage Confirmation Stage

NOTE: You must use the buttons in the Confirmation Stage

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A B C D

Radiation fog Advection fog

Question #3 -

What fog forms when warm moist air moves over a cold surface?

Upslope fog Frontal fog

Meteorology Meteorology

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Forms when warm moist air

moves over a cold surface.

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A B C D

Radiation fog

Precipitation-induced fog

Question #4 -

What fog forms when cold air passes over a warm water surface. Evaporation of the water into the cold air occurs until the air becomes saturated. The excess water vapour

condenses as fog.

Upslope fog Steam fog

Meteorology Meteorology

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Forms when cold air passes over a warm water surface. Evaporation of the water into the cold air occurs until the air becomes saturated. The excess water vapour condenses as fog.

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Congratulations!!

You have now completed the Clouds, Precipitation & Fog lesson of the Meteorology Module. Of course, this lesson is always available to you for future reference if required.

You are now ready to move along to the next Meteorology lesson you have not completed or to any other module you wish. You can advance to the Self Test Module if you feel ready to challenge the final exam.

Good Luck!