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Weather UnitWeather Unit
Whether it
is climate
or not?

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Today we will look at …Today we will look at …
1. What makes weather?
2. How do we measure weather?
3. Why do we need forecasts?
4. Are the forecasts any good? (that’s
homework)

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What is the weather?What is the weather?
Weather is the condition of the
air around us over a short
period of time (from day to day)

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The elements of weatherThe elements of weather
Temperature (the amount of heat)
Precipitation (water – rain, sleet, hail,
snow)
Wind speed
Wind direction
Clouds
Air pressure
Visibility (How far can you see?)

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TemperatureTemperature
This is a measure of
how hot or cold it is.
We can tell this by
looking at the clothes
that people wear.

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PrecipitationPrecipitation
Water in the air falls
to the ground in one
of several forms
Rain
Snow
Sleet
Hail
But also ice and fog

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Wind SpeedWind Speed
This tells us how
strong the wind is.
We can get a good
ideas of this by
looking at smoke
and trees.

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Wind directionWind direction
This is the
direction from
which the wind
blows – it is
measured by a
wind vane

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Cloud TypeCloud Type
Clouds come in many
shapes, sizes and
heights – more about
that next week

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Cloud CoverCloud Cover
This is the amount of
the sky covered by
cloud. It is
measured in eighths
Clear sky
4/8
8/8 (Total cover)

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VisibilityVisibility
This is the distance
that can be seen. It
is measured in
metres.

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Measuring WeatherMeasuring Weather
Why do we measure the weather?
Weather can be described using terms such as wet or
fine, warm or cold, windy or calm, so why is there a
need to measure the weather?
For most people, a description of the weather is
adequate but for many businesses more detailed and
accurate measurements are required.
The science of studying weather is called meteorology.
Weather scientists or meteorologists measure
temperature, rainfall, pressure, humidity, sunshine and
cloudiness and they make predictions and forecasts
about what the weather will do in the future.
This is important for giving people advance notice of
severe weather such as floods and hurricanes – or even
‘Can I go out without my raincoat tomorrow?’
Who else might
find a forecast
useful?

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Measuring temperatureMeasuring temperature
The hotness or coldness of a substance is called its
temperature and is measured with a thermometer. The
ordinary thermometer consists of a hollow glass bulb
attached to a narrow stem with a thread-like bore.
The bulb is filled with liquid,
– If it is silver it is mercury
– If it is red it is alcohol
The liquid in the tube expands when the temperature
rises and contracts when the temperature falls. The
amount of expansion and contraction is measured by a
numbered scale.
Whilst thermometers are really measuring their own
temperature, they are used to measure the
temperature of the surrounding air.
To make sure that the temperature of the surrounding
air is the same as the thermometer, it must be shaded
from sunlight and be exposed to adequate ventilation.
These conditions are provided by a Stevenson screen.

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A Stevenson screenA Stevenson screen
Why do we need
one of these?
Why does it
have legs?
Why is it painted
white?
Why has it got such a large
roof?
What are the
little gaps in
the side for?
(louvers)

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Measuring temperatureMeasuring temperature
Most temperature scales today are
expressed in degrees Celsius (°C),
although you will sometime see
Fahrenheit (°F) in use.
The Celsius scale is fixed by two points,
the freezing and boiling point of water,
which at sea level are 0°C and 100°C
respectively.
The scale is then divided into 100 units.

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Measuring TemperatureMeasuring Temperature
This is a maximum-minimum
thermometer.
This type of thermometer
measures both the highest
(maximum) and lowest (minimum)
temperature over a period of time,
usually one day (24 hours).
Recording temperature with a
maximum-minimum thermometer
There are two markers, one for
the maximum temperature and one
for the minimum. The mercury in
the tube pushes the markers as
temperatures go up or down.

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Measuring TemperatureMeasuring Temperature
The temperature tends to be highest around
the middle of the day, when the sun is at its
hottest – even if you cannot see it because it is
cloudy
The temperature is coldest during the night
So if you leave a maxi-min thermometer for 24
hours you will get the maximum and the
minimum and be able to find the daily range
(the difference between the 2)
The difference between the daily maximum
and the daily minimum temperature is the
diurnal range.

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Looking at the first 2 rows on theLooking at the first 2 rows on the
WSWS
What does a thermometer do?
How does it work?
What does a maxi-min thermometer tell
you?
What is diurnal range?
What does a Stevenson screen do?
How does it work?

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Wind speedWind speed
Wind is moving air.
Wind can be measured by its speed
and the direction from which it has
come.
The speed of the wind can be
measured using a weather instrument
called an anemometer.
The speed can be recorded in many
different units, including for
example:
– miles per hour;
– kilometres per hour;
– metres per second;
– knots;
– the Beaufort Scale (we will learn about
this one next week)
This one has
a weather
vane on it
underneath.
What does
that tell
you?

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Wind directionWind direction
The direction of the wind is expressed as the
point on the compass from where the wind is
blowing.
If a wind is blowing from the south, it is
travelling northwards but is called a southerly
wind.
Wind direction can be measured in many
different ways; using a weather vane or simply
holding a light object such as a flag or ribbon.
On your sheet, write down what they are
smelling!!
http://www.bbc.co.uk/schools/whatisweather/abou

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Wind directionWind direction
Knowledge of wind direction is important
for many people and activities.
For example aircraft need to take off
from the end of the runway which is
going into the wind for extra lift at
take-off
Wind direction is of course very
important for leisure activities such as
yachting.
Can you think of anything else where
knowing the wind direction is important

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For the WS…For the WS…
What is an anemometer for?
How does it work?
What is a weather vane for?
How does it work?

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Air pressureAir pressure
An instrument called a
barometer is used to
measure the pressure of
air.
Although air is very light,
because the atmosphere is
so thick (many kilometres in
altitude above the Earth's
surface), air exerts a force
or pressure.
When air is cooled it sinks
towards the ground, the
pressure increases and a
high pressure is measured.
When the air warms up it
rises, the pressure is
reduced and low pressure is
measured.
This is what goes on
inside a barometer

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Air pressureAir pressure
Why do we need to know
about pressure?
High pressure gives us
clear skies which means it
is hot in the summer and
cold in the winter
Low pressure gives us
cloudy skies and rain. We
have lots of low pressure
over the summer in the UK!

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For the WSFor the WS
What is a barometer for?
How does it work?
What is weather like if the pressure is
high in summer?
What is the weather like if the pressure
is low?

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Measuring liquid precipitationMeasuring liquid precipitation
What varieties of precipitation are
there?
Which types are NOT liquid?
Why do you think that if we measured
this one, that we might not use the same
instrument as the liquid one?

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This is the rain gauge used by theThis is the rain gauge used by the
Met OfficeMet Office Why do you
think the actual
funnel is inside a
copper cylinder
– not a the top?
Why is the bottle
that stores the water
underground?
How does the
measuring gauge
on the right work?

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For the WS…For the WS…
What is a rain gauge for?
What kind of precipitation does it not
collect?

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Weather is important to usWeather is important to us
Things that are affected by weather
– farming
– sport
– transport
– the amount of energy we use
– work
– tourism

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So we need weather forecastsSo we need weather forecasts
Information is
collected by
– weather stations
– http://www.weatherstations.co.uk/aws_map.htm
Often schools have
them

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So we need weather forecastsSo we need weather forecasts
Information is also
collected by
By ships
Aircraft
Satellites
and then the
meteorologists use
the information they
have to predict the
weather over the
next few days

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Weather from the met officeWeather from the met office
Friday’s map from
http://www.met-office.gov.uk/weather/europe/uk

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Weather from the met officeWeather from the met office
This was the wind
map. The numbers
measure in miles per
hour with direction it
is blowing to
http://www.met-office.gov.uk/weather/europe/uk

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Weather from the met officeWeather from the met office
This was the
Temperature map.
The numbers
measure in degrees
centigrade
http://www.met-office.gov.uk/weather/europe/uk

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And BBC weatherAnd BBC weather
From
http://www.bbc.co.uk/weather/ukweather/index.shtml
It used to show it all on
but now they just show
where the cloud is!!

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And weather onlineAnd weather online
From
http://www.weat
heronline.co.uk
Does show it all
except the wind
speed and
direction!!

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Symbols are
different but
once you get the
idea…
So what is the
weather
supposed to be
like in each of
these places?

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HomeworkHomework
Go to (hopefully now!)
http://www.weatheronline.co.uk/
Click either UK or
your continent
If it is the UK, click
on your region
Do not go more
detailed than that
If a continent, pick
which part, then pick
your country

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Now you have got your weatherNow you have got your weather
forecastforecast
Look out each day – how good was the
forecast?
If you have a thermometer, do use it and
add that information in!
If you haven’t, not to worry.
Having put your pictures into the table
Record the weather you had in the
middle column