ATPL Meteorology - Class 6: Clouds.

Summary

This meteorology class explores cloud formation, starting with the basics of condensation and the dew point. It explains how clouds form from air cooling and water vapor condensing, influenced by dry and saturated adiabatic lapse rates. The video covers various cloud types, from high-level cirrus to low-level cumulonimbus, and their association with weather conditions. It also discusses cloud stability, the environmental lapse rate, and how these factors affect cloud cover and visibility for pilots, concluding with the significance of cloud classification in weather reports.

Takeaways

• 🌧️ Clouds form due to the process of condensation, where water vapor cools and changes from a gas to a liquid state.
• 🌡️ The dew point is the temperature at which air reaches saturation and water vapor starts to condense.
• 🧊 If the dew point is below freezing, water vapor can sublimate directly into ice crystals, forming around impurities or remaining as supercooled droplets until an impurity is introduced.
• 🌬️ Adiabatic cooling occurs when air expands and cools due to a drop in pressure, separate from the cooling caused by the surface temperature.
• ⬆️ As air rises, it cools at a rate of 3 degrees per thousand feet (dry adiabatic lapse rate) until it reaches the dew point, after which it cools at 1.8 degrees per thousand feet (saturated adiabatic lapse rate).
• 🌫️ Fog and mist are forms of low clouds that form when air is cooled near the surface, rather than through adiabatic rising.
• 🏞️ Air rises due to being warmer, orographic lifting by geographic features, or when encountering a front of colder, denser air.
• 🌟 Stability of air is determined by comparing the environmental lapse rate to the adiabatic lapse rates, which affects whether air will continue to rise, sink, or remain stable.
• 🌦️ Clouds are categorized by their stability (stable or unstable), height (low, mid, high), shape (stratiform or cumuliform), and the type of precipitation they produce.
• 📊 Cloud cover at aerodromes is reported in 'oktas', with full coverage being overcast and clear skies reported as 'SKC'.

Q & A

What is the fundamental concept behind cloud formation?

The fundamental concept behind cloud formation is condensation, which is the process of water vapor cooling to the point where it changes from a gas to a liquid state.

What is the dew point and how does it relate to cloud formation?

The dew point is the temperature at which the saturation vapor pressure matches the actual amount of water vapor in the air, leading to condensation. This is where water vapor starts to condense, marking the beginning of cloud formation.

How does the temperature change as air rises and its effect on cloud formation?

As air rises, the pressure drops, causing the air to expand and cool. This cooling is known as adiabatic cooling, which occurs at a rate of 3 degrees per thousand feet for dry air and 1.8 degrees per thousand feet for saturated air, influencing cloud formation.

What is the difference between dry and saturated adiabatic lapse rates?

The dry adiabatic lapse rate is 3 degrees per thousand feet and occurs when the air is not saturated, while the saturated adiabatic lapse rate is 1.8 degrees per thousand feet and occurs when the air is saturated and water vapor starts to condense.

Why do clouds form at different altitudes?

Clouds form at different altitudes based on the temperature and dew point. The altitude at which the air cools to the dew point determines the cloud base, with different types of clouds forming at low, mid, and high levels.

What role do impurities play in the formation of ice crystals in clouds?

Impurities in the air, such as smog particles or dust, provide a surface for ice crystals to form when the temperature is below freezing. Without impurities, supercooled water droplets may form and only freeze when they encounter an impurity.

How does the environmental lapse rate affect the stability of the atmosphere and cloud formation?

The environmental lapse rate compares to the adiabatic lapse rates to determine atmospheric stability. If it's lower than both dry and saturated adiabatic lapse rates, the atmosphere is stable, but if it's higher, the atmosphere is unstable, leading to more cloud formation.

What are the two broad categories of clouds and how do they differ?

The two broad categories of clouds are stable and unstable. Stable clouds are widespread and low, associated with light precipitation, while unstable clouds are tall and fluffy, associated with heavier showers and turbulence.

How are clouds classified by height and what are the categories?

Clouds are classified by height into low-level clouds (up to 6,500 feet), mid-level clouds (6,500 to 23,000 feet), and high-level clouds (above 23,000 feet).

What does it mean when clouds are described in terms of 'octas' in aviation?

In aviation, clouds are described in terms of 'octas' or eighths to indicate the amount of sky covered by clouds overhead an aerodrome, ranging from clear sky to overcast.

Outlines

00:00

🌟 Introduction to Cloud Formation

The paragraph introduces the topic of cloud formation, explaining the process of condensation where water vapor cools down and changes from gas to liquid form. The dew point, the temperature at which air can no longer hold water vapor and condensation occurs, is discussed. The text also covers the concepts of adiabatic cooling, where air cools as it rises due to reduced pressure, and the different lapse rates for dry and saturated air. The importance of understanding humidity is emphasized, and the viewer is encouraged to review previous content on this topic.

05:00

🌤️ Estimating Cloud Base and Fog Formation

This section delves into how to estimate the cloud base using temperature and dew point data, and discusses the formation of fog and mist. It explains that fog forms when air is cooled by a cold surface, leading to condensation without the need for air to rise. The difference between fog and mist is also clarified, based on visibility levels. The paragraph further explores why air parcels rise, including due to temperature differences or geographic features like mountains, and introduces the concept of atmospheric stability, which affects cloud formation.

10:03

🌡️ Atmospheric Stability and Cloud Types

The paragraph discusses the three types of atmospheric stability: absolute stability, absolute instability, and conditional stability, which depend on the environmental lapse rate compared to the adiabatic lapse rates. It explains how these conditions affect whether air parcels rise or sink. The categorization of clouds into stable (stratiform) and unstable (cumuliform) types is introduced, along with the basic characteristics of these cloud forms. The importance of understanding cloud types for pilots, in terms of weather conditions and visibility, is highlighted.

15:04

☁️ Detailed Cloud Classification

This section provides a detailed classification of clouds based on height (low, mid, high), shape (stratiform, cumuliform), and the type of precipitation they produce. It describes various cloud types, including cirrus, altostratus, altocumulus, nimbostratus, stratus, stratocumulus, and cumulus, along with their associated weather conditions. The paragraph emphasizes the importance of cloud cover reporting in eighths for pilots, which helps in assessing weather conditions at aerodromes.

20:06

🌦️ Cloud Cover and Weather Reporting

The final paragraph summarizes the importance of condensation at the dew point and adiabatic cooling in cloud formation. It revisits the concepts of stability and instability in the atmosphere and their impact on cloud formation. The classification of clouds is reiterated, with a reminder of the various types and their characteristics. The paragraph concludes with a discussion on cloud cover reporting in terms of octas (eighths of the sky) and the distinction between cloud ceiling and cloud base, which are crucial for aviation weather reports.

Keywords

💡Condensation

Condensation is the process by which water vapor in the air cools down to the point where it changes from a gas to a liquid state. This is a fundamental concept in the formation of clouds, as explained in the video. When air cools, water molecules lose energy and start to clump together, forming tiny liquid droplets that we see as clouds. The video mentions that condensation occurs at the dew point, which is the temperature at which the air can no longer hold all the water vapor it contains, leading to the formation of clouds.

💡Dew Point

The dew point is the temperature at which air becomes saturated with water vapor and can no longer hold all the moisture it contains, leading to condensation. In the context of the video, the dew point is crucial for understanding cloud formation. When the temperature of the air reaches the dew point, water vapor starts to condense into liquid water, forming clouds. The video provides an example where a dew point of 10 degrees Celsius would lead to the formation of liquid water droplets in the air.

💡Adiabatic Cooling

Adiabatic cooling refers to the cooling of air that occurs due to its expansion, without any exchange of heat with the surroundings. This is a key process in meteorology that influences cloud formation. As air rises, it expands due to the decrease in atmospheric pressure, leading to a drop in temperature. The video explains that this cooling happens at a rate of three degrees per thousand feet for dry air (dry adiabatic lapse rate) and 1.8 degrees per thousand feet for saturated air (saturated adiabatic lapse rate), which is critical for determining cloud formation and types.

💡Cloud Formation

Cloud formation is the process by which visible masses of water droplets or ice crystals suspended in the atmosphere come together. The video explains that this happens when air rises and cools to the dew point, causing water vapor to condense. The script describes how different conditions, such as temperature and air pressure, affect the type of clouds formed, and how they can be described and categorized based on their appearance and altitude.

💡Saturated Adiabatic Lapse Rate

The saturated adiabatic lapse rate is the rate at which air temperature decreases as it rises and cools due to expansion when the air is saturated with water vapor. As described in the video, this rate is 1.8 degrees per thousand feet. It is slower than the dry adiabatic lapse rate because the release of latent heat during condensation warms the air, thus reducing the rate of temperature decrease. This concept is essential for understanding how clouds continue to form as air rises and cools.

💡Cirrus Clouds

Cirrus clouds are high-level clouds that appear as thin, wispy strands, often mistaken for patches of smoke in the sky. They are typically associated with fair weather but can also be an indicator of an approaching weather system. The video mentions cirrus clouds as an example of high-level clouds that form under stable atmospheric conditions and do not produce precipitation.

💡Cumulus Clouds

Cumulus clouds are low-level, puffy clouds that often resemble cotton balls. They are associated with unstable atmospheric conditions and can lead to showers or thunderstorms. The video describes cumulus clouds as an example of clouds that form due to rising warm air and can result in moderate showers if precipitation occurs.

💡Stratus Clouds

Stratus clouds are low-level, gray clouds that often cover the entire sky, creating an overcast appearance. They are associated with stable atmospheric conditions and can produce light, continuous precipitation. The video explains that stratus clouds form when air cools and water vapor condenses near the ground, leading to a uniform cloud layer.

💡Orographic Lifting

Orographic lifting is the process by which air is forced to rise and cool when it encounters a geographic feature such as a mountain range. This can lead to condensation and cloud formation. The video mentions orographic lifting as one of the ways air can be lifted, causing clouds to form as the air mass is forced upwards by the terrain.

💡Cloud Cover

Cloud cover refers to the amount of the sky that is obscured by clouds. It is an important factor in weather forecasting and aviation. The video explains that cloud cover is reported in 'octas' or eighths, with each eighth representing a portion of the sky. This information is crucial for pilots to determine visibility and weather conditions at aerodromes.

Highlights

Clouds form due to condensation, where water vapor cools and changes from gas to liquid form.

The dew point is the temperature at which air reaches saturation and water vapor starts to condense.

Sublimation occurs when the dew point is below zero degrees Celsius, leading to the formation of ice crystals.

Supercooled water droplets form when there are very few impurities in the air, and they can remain liquid below freezing point.

Adiabatic cooling is a secondary temperature reduction caused by the expansion of air as it rises.

The dry adiabatic lapse rate is 3 degrees Celsius per thousand feet, indicating the rate of cooling due to adiabatic expansion in dry air.

The saturated adiabatic lapse rate is 1.8 degrees Celsius per thousand feet, which applies when air is saturated with water vapor.

Clouds are formed as air parcels rise and cool adiabatically, condensing water vapor at the dew point.

Fog or mist is a low cloud formed when air is cooled at the surface, without the adiabatic rising process.

Air rises due to being warmer, or due to geographic features like mountains, or when it encounters a colder air mass.

Stability of air is determined by comparing the environmental lapse rate with the adiabatic lapse rates.

Absolute stability occurs when the environmental lapse rate is lower than both adiabatic lapse rates, leading to sinking air.

Absolute instability happens when the environmental lapse rate is higher than both adiabatic lapse rates, causing air to rise.

Conditional stability depends on whether the air is dry or saturated, influencing whether air rises or sinks.

Clouds are categorized by height into low, mid, and high level clouds, and by shape into stratiform or cumuliform.

Cirrus, altostratus, and nimbostratus are examples of clouds associated with stable weather conditions.

Cumulus and cumulonimbus clouds are associated with unstable conditions and can lead to showers and thunderstorms.

Cloud cover is reported in eighths, or octas, to describe the amount of sky covered by clouds at an aerodrome.

Cloud base and cloud ceiling are terms used to describe the height of the lowest and highest clouds respectively.

Transcripts

i'm sure we have all looked for cool

shapes and objects in the clouds when we

were younger i know i did at least but

how do these cool shapes and objects

form in the sky

let's find out

[Music]

hi i'm grant and welcome to the sixth

class in the meteorology series we've

now finished looking at the basic

elements of the atmosphere we're going

to be moving on to the more interesting

weather aspect of meteorology

in this class we're going to be taking a

look at how clouds are formed and how we

describe them and this class requires a

good understanding of how humidity works

so if you haven't done so i'd recommend

going back and watching the previous

video all about humidity before getting

started on this one

the fundamental concept behind why

clouds form is due to condensation which

is the process of water vapor cooling to

the point where it is no longer in gas

form but now in liquid form

this happens because the air cools down

and the individual water molecules lose

energy and start to be attracted to each

other and when the particles are close

together they form chains of these

particles which in on the atomic level

is how

liquid states are formed so that's why

we get liquid water when we cool down

the temperature at which this

condensation occurs is known as the dew

point

this is the temperature where the

saturation vapor pressure the amount of

water the air that can hold what amount

of water vapor the air can hold

reduces down to the point where it

matches the actual amount of water in

the air known as the actual water vapor

pressure

when the temperature of this dew point

is above zero degrees celsius in this

example we've chosen 10 degrees celsius

we would form

it's the

liquid water molecules in the air

if the dew point was below

zero degrees celsius then we would

sublimate we would go through the

sublimation process

straight into the solid water state in

ice form ice crystals form around

impurities in the air

so if you're in the situation where

there are very few impurities near such

as like smog particles or dust particles

then you can end up with something

called supercooled water droplets

and these are just extremely cold

droplets of water

and they will only form into ice when an

impurity is introduced

this can happen for example when an

aircraft flies through a cloud full of

super cold water droplets that aircraft

is then the impurity in the air that the

supercooled water droplets would need to

form ice and that could be maybe the

leading edge of the wing for example

when air rises the pressure drops and so

does the temperature as we get further

and further from the surface

because of the pressure drop the air

will also expand because there's

obviously less pressure to push it all

together

if we ignore the temperature reduction

caused by moving away from the surface

and only look at the pressure reduction

there is then a secondary temperature

reduction which is caused by the

expansion of the air

this secondary temperature reduction

happens all the time as parcels of air

rise and fall and it happens

independently of this actual temperature

changes

caused by the surface being warmer than

it is higher up

and this secondary temperature cooling

process

we call an adiabatic cooling process

adiabatic

so as a parcel of air rises and cools

adiabatically due to that expanding

air and dropping pressure it does this

at a rate of three degrees per thousand

feet so if we have a parcel of air

rising up every thousand feet that

parcel of air will cool just because of

the secondary effect by three degrees

every thousand feet this is known as the

dry adiabatic latch rate

so it's dry because it's

below the saturated humidity it's below

a relative humidity of 100

when it cools down to the dew point and

the air now becomes saturated it then

cools adiabatically at a different rate

which is known as the saturated

adiabatic lapse rate and this is 1.8

degrees per thousand feet the reason

behind this difference is because as the

water vapor starts to condense out into

liquid form at the dew point the heat is

given off heat is released in order to

change it to this liquid state and this

heating effect this heat being given off

um adjusts the temperature from 3

degrees up to 1.8 there's that latent

heat in the atmosphere that is stopping

it from three degrees and moving it more

towards 1.8

so hopefully you can start to see the

way that clouds are formed a parcel of

air rises up and cools down

adiabatically at the dry adiabatic lapse

rate of three degrees per thousand feet

this is until it reaches

the temperature where the air cannot

hold any more water vapor in it and it

becomes saturated the dew point

temperature

the water vapor then condenses out to

form the beginnings of clouds and as the

parcel of air continues to rise at the

saturated adiabatic lapse rate

of 1.8 per thousand feet

it paints more cloud as it goes just a

little paintbrush painting clouds as it

goes this means that you can estimate

the cloud base if you know the current

temperature and the dew point

in this example we're going from a

temperature of 16 degrees celsius and we

know that the dew point is 4 degrees

celsius

so it's a 12 degree change and we're

doing 3 degrees every thousand feet we

can estimate that the cloud base is

going to be up at 4 000 feet the actual

height of the clouds will depend very

much on the stability of the atmosphere

which we'll look at in a little bit

fog or mist is just very low cloud and

it's formed slightly differently to

regular clouds the main difference is

that the adiabatic rising and expanding

process doesn't occur

because the air isn't rising essentially

with fog the air is cooled down because

of a cold surface temperature through

conduction and radiation heating and

stuff like that

with fog the air is cooled because of

the cold temperature and that brings the

saturation vapor pressure down until it

meets the actual amount of water vapor

pressure in the air which is known as

the dew point

at this dew point all the water vapor in

the air condenses out to form clouds and

the small water and ice particles are

lifted and mixed through the air by wind

and the cool surrounding air causes yet

more

water vapor to condense out

and depending on the temperature and the

amount of mixing going on fog can be a

couple of feet off the ground to a

couple of hundred or a couple of

thousand feet even

the only difference between mist and fog

is the level of visibility inside it

fog is considered the visibility less

than a thousand meters and missed is

when the visibility is less than 5000

meters

so why does a parcel of air rise

the most basic one is considering warm

air

so warm air rises because it expands the

volume increases and that makes the

density decrease

and less dense things float on top of

more dense things so hot air will rise

because of this reason

air can also be caused to rise by

geographic features such as mountains

which is known as orographic rising

another way that it can rise is when you

reach the

front of a colder band of air colder air

is more dense and you come in the air

comes in not you come in the parcel of

air comes in and is will automatically

be

less dense than a colder section of air

so it will rise up because of that

depending on the relative density

of the air

compared to its surroundings it will

either continue to rise known as

unstable air it will descend which is

known as stable air or it will stay

exactly where it is in neutral

equilibrium

the density of the surrounding air is

also going to be dependent on

temperature such as the heating process

that we saw

and the way that this works is that the

rising parcel of air will cool at the

dry adiabatic lapse rate or the

saturated

adiabatic lapse rate

and we compare that to what is known as

the environmental lapse rate

so this would be

um if we're looking at our international

standard atmosphere this is the two

degrees per thousand feet

but

depending on the day and the conditions

this is going to be slightly different

so when we compare these two we can find

out if the saturated sorry if the rising

parcel of air is more dense or less

dense compared to its surroundings and

if it is less dense it will continue to

rise and if it is more dense it will

start to sink down and be more stable

so the best way to think about these

stability in general is to compare the

three main types

the first one is known as absolute

stability

so this means that the temperature of

the parcel of air must always be

warmer than

the

environmental air surrounding it

so in this diagram here we've used an

environmental latte of one degrees per

thousand feet

this means that as a parcel of air rises

it will always be cooling down at a

faster rate of either three degrees for

the dry

or 1.8 for the saturated

this means that wherever we look at the

altitude the rising parcel of air is

always going to be

colder and therefore more dense

and it will tend to sink rather than

rise

so for absolute stability you need the

environmental latch rate to be lower

than both the saturated and the dry

adiabatic lapse rate

one degree needs to be below 1.8 in

essence

the opposite case to this is absolute

instability

this means that the temperature of the

parcel of air must always be hotter than

the surrounding environmental air to

make it less dense and to rise up

this happens when the environmental

artery is larger than both the dry and

saturated adiabatic lapse rate

so if we have look at this example and

we have an environmental latte of four

degrees every thousand feet

then if we start off at a sea level

temperature of 18

the rising parcel of air will reach a

temperature of

12 degrees at 2 000 feet because it's

three degrees every thousand feet six

degree difference

while the surrounding air

will cool down to 10 degrees

because it's cooling four degrees every

thousand feet

this means that our

parcel of air that's rising is hotter

and it's going to continue to rise when

the air becomes saturated it then starts

to cool up 1.8 degrees per thousand feet

and by the time we reach 4000 feet we're

going to be at

8.4 degrees

and by this point the surrounding air is

going to be all the way down at 2

degrees

so again the rising parcel of air is

warmer it will continue to rise the

third type of stability is conditional

stability and this is can the condition

in this case is whether the air is dry

or saturated so if the parcel of air is

unsaturated it will be colder than the

surrounding air

and it therefore sinks down

if the parcel of air is saturated it

will then become warmer than the

surrounding air and keep rising

this will happen when the environmental

artery is between the dry and saturated

adiabatic lapse rate

if we think about it in this example of

two degrees for every thousand feet

then if we start at a temperature of 10

degrees celsius at 2000 feet we're going

to be at

4 degrees celsius

and the surrounding air the

environmental lapse rate will be six

degrees celsius

so

the rising parcel of air is more dense

it will tend to sink down

once we become saturated however

the temperature would only drop by 1.8

degrees and it would start to become

initially it will be

reducing the gap between them and

eventually they will cross over

and the environmental lapse rate

and the saturated adiabatic lapse rate

will

flip in essence and you'll have the

rising parcel of air always be warmer

than the environmental lapse rate and it

will continue to rise

as humans we like to categorize things

and clouds are no different

generally speaking though they fall into

two broad categories which are either

stable or unstable

stable clouds will be what we call

stratiform which means very

short not very tall and very widespread

they are associated with light

continuous precipitation

poor visibility and light turbulence

because there's not that much air rising

to cause that turbulence

the other type is unstable clouds which

are what we call cumulform

which means they're tall and fluffy

basically

they're also associated with showers of

precipitation

but good visibility but again we've got

that moderate to heavy turbulence

because there's lots of air rising to

cause it

you'll never really hear cloud types

described as stable or unstable

and because there's a lot more specifics

that we can get into as you can see

the first one to talk about is the

height of clouds

if the cloud base the bottom of the

cloud is up to six thousand five hundred

feet we call these low level mid level

is six thousand five hundred to two

twenty three thousand

and high level clouds would be above

twenty three thousand then you can

describe them again in terms of shape

in terms of cirrus which means like

quite wispy

or cumulus which means that kind of

fluffy shape that you would typically

think of when you think of a cloud and

then you can

combine and cross different types of

these clouds to form the main categories

here as i'll quickly run through

i've tried to draw them very badly so

it's probably if you're very interested

to see what type they are just have a

quick google and you'll see that my

drawings are rubbish so starting off

with the high level clouds cirrus clouds

cirrostratus and cirrocumulus

so cirrus are like feathery sort of

shapes

and

cereal stratus are like mesh of fibers

kind of like a hazy sort of look

and ciro cumulus are small bubbly clouds

and they're all con associated with

relatively stable conditions apart from

the serocumulus which will have little

unstable patches where the little

bubbles fall

and because they're so high up there's

no precipitation from any of them

mid-level clouds have the prefix of alto

that's a good way to remember mid-level

clouds and they fall into either the

strata form or the cumulative form

stratiform being the low

and widespread and cumulative form being

more fluffy more um more height to them

so altostratus would be kind of grey

blue colours and quite large associated

with stable conditions and maybe give

you some light continuous precipitation

altocumulus would be white gray with a

few bumps of cumulus looking things

and that means that there's going to be

unstable little parts within it

and that's associated with light showers

as well then you come on to the

low-level clouds where you see a lot of

precipitation this is where most of the

precipitation is formed

first one of these is nimble stratus

that's your kind of gray

and overcast condition sort of clouds

associated with stable conditions and

you'd get moderate continuous

precipitation out of them

you could have stratus clouds as well

that's a

a gray sort of layer

to be quite stable conditions and you

get continuous light so not as

developed as a nimbo stratus think of

that as like a rain cloud continuous

rain all day that may be a chance of

rain

stratocumulus clouds are patchy white

and that means there's a few unstable

patches and you have the potential for

continuous light precipitation

cumulus clouds are your fluffy low

clouds good for you know spotting shapes

in and stuff like that

associated with unstable conditions

and expect moderate showers if any

precipitation

and then the daddy of them all

cumulonimbus clouds these are your big

high developed putting them in a low

level cloud because of the low base but

they can extend all the way up to the

levels of high level

they can be

all the way up to the

uh troposphere tropopause even

uh up to that you know 36 000 feet these

can be very very large clouds

and

they are storm clouds essentially very

unstable associated with heavy showers

lightning

uh not in good conditions basically so

there's a whole world of cloud types and

classifications to jump into if you're

interested but an important factor for

us pilots is the amount of cloud cover

we would like to know if it's going to

be a blue sky day or overcast so we

basically know when to pack our nice

sunglasses or not

it's also kind of useful for telling us

the weather conditions at an aerodrome

so

we will then be able to work out if we

are able to land there or not

the cloud cover is reported to us in

terms of eighths of the sky

overhead the aerodrome which is known as

an octa one-eighth is equal to one octa

and if you imagine this is the the land

that the aerodrome takes up just divide

that into eight sections and that is how

you decide how much cloud cover is

overhead in aerodrome this is something

we're gonna get into a bit more in terms

of when we look at weather reports

towards the end of this uh series

but just for now know that it's eighths

of the sky and there's different regions

uh different ranges for

the amount of cloud cover you get zero

which is known as clear sky sky clear

skc is given a little designator on

weather reports one to two is few three

to four is scattered five to seven is

broken and eight is overcast

and if the sky is more than fifty

percent covered so these bottom two

you call it a cloud ceiling

whereas if it's the

uh below fifty percent ones zero one

well not zero but one to two or three to

four you would call that a cloud base

so you would see a report on airdrome

will tell you various weathers and i

would say

there's few clouds at

1500 feet so you could say the cloud

base is at 1500 feet

in summary then so condensation happens

at the dew point and this is where the

saturation vapor pressure

reduces to the actual vapor pressure

that we have in the air and the water

starts to condense out

if the dew point is lower than zero then

the water can sublimate straight into

ice and these ice crystals will form

around impurities if there's no

impurities it will sublimate uh well it

won't submit it will just form very cold

extremely cold supercooled water

droplets which will then form ice when

introduced to an impurity such as an

aircraft

adiabatic cooling is the separate

secondary cooling which is caused by the

expansion of air think of it as like

when you

spray a can of if you've got compressed

air for cleaning out a computer or

something like that that gets very cold

because the air is expanding and cooling

down

the rate of cooling that happens with

this expansion is dependent on the air

and if it's dry or if it's saturated the

dry adiabatic latte is three degrees per

thousand feet and the saturated

adiabatic latter is 1.8 degrees per

thousand feet clouds form

by these

air pockets these parcels of airs

cooling down to the dew point due to

that dry adiabatic lapse rate due to

rising of that dry adiabatic labs rate

and then they will continue to rise at

the saturated adiabatic lapse rate and

depending on the environmental lapse

rate will either have

stable conditions

in stable conditions or conditional

conditions

so absolute stability is when the

environmental latter ray is lower than

both the saturated and the dry adiabatic

latex rate so that means it's going to

be a value of less than 1.8 degrees per

thousand feet that means that the

temperature of the air parcel is always

going to be colder than the surrounding

environmental air and therefore more

dense and it's going to be

more stable

the opposite of that is absolute

instability

when the air

environmental latch rate is larger than

the dry adiabatic latex rate and the

saturated adiabatic lapse rate and that

means that a rising parcel of air the

dry or saturated rising parcel of air is

always going to be warmer than the

surrounding air less dense it's going to

rise up

and then you've got conditional which is

between the two

and basically depends if the air is dry

it will be more stable and if it's

saturated it will become it unstable

clouds can be classified in loads of

different ways

and there's basically a few categories

that you think if you think of a stable

versus unstable stable

low

widespread clouds unstable quite high

fluffy clouds then you think about the

height you've got the low mid or high

levels think about the shape

you've got the stratiform shape or

you've got the cumulo

cumulus shape

then you've got the types of

precipitation

and

nimble usually means

wet i don't know what the actual word

means but if it's nimble stratus that

means it's going to be moderate

um

moderate rain whereas if it's just a

stratus it might not be quite as heavy

rain

classification is a bit weird because

there's a lot of crossover and it's hard

to tell

when a stratus becomes a nimble stratus

there's no like defining thing

so

cloud classification come with a pinch

of salt

and then when we're looking at cloud

reports or weather reports for

aerodromes we'll see it described in

terms of octas which means eighths and

if the aerodrome is covered by no clouds

you will say it's sky clear

if it's one to two of these eights that

are covered it'd be few three to four is

scattered five to seven is broken and

eight is overcast

and when there's more than 50 percent of

the

uh space over the air drone covered in

clouds is known as a cloud ceiling so

broken and over classic cloud ceiling

and

not sky clear because obviously there's

none but one

to four few and scattered you would call

that a cloud base