seegongsik
Grade 6 (age 11-12)

grade 6 Weather Forecasting

When you check the forecast in the morning and decide whether to take an umbrella, you are relying on people who measured the weather ahead of you. A weather service records air temperature with thermometers, the water vapour in the air with hygrometers, and the direction the wind comes from and how much rain falls with wind vanes and rain gauges. Air that holds a lot of water vapour forms clouds easily; under high pressure air sinks and skies are usually clear, while under low pressure air rises and it turns cloudy or rainy. On this page you read what each instrument shows, then change the humidity and the pressure difference to see how clouds and wind change.

What do we measure the weather with?

🌡️ What the instruments measure
①A thermometer measures air temperature in °C
②A wind vane shows the direction the wind comes from: a wind blowing from the north is a north wind
③An anemometer measures wind speed in m/s
④A rain gauge measures rainfall in mm, from the depth of water that collects in it
⑤A hygrometer shows how much water vapour the air holds, as a percentage

Water vapour, clouds and rain

40%
☁️ From water vapour to cloud
①The more water vapour the air holds, in other words the higher the humidity, the more easily clouds form
②When moist air rises and cools, the vapour condenses into tiny water droplets or ice crystals, and a mass of these is a cloud
③When the droplets in a cloud grow large and heavy, they fall as rain or snow
④That is why, as you raise the humidity in the picture, the sun disappears, the clouds thicken and then rain falls

High pressure, low pressure and the wind between

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🗺️ High pressure, low pressure and wind
①A place where the air pressure is higher than around it is a high, and where it is lower is a low
②In a high, air sinks and clouds break up, so the sky is usually clear
③In a low, air rises and cools and clouds form, so it is cloudy or rainy
④Wind blows from high pressure towards low pressure
⑤Isobars are lines joining places with the same pressure. The bigger the pressure difference, the closer together the isobars and the stronger the wind

Summary

What makes up the weather
temperature + humidity + wind + rainfall + pressure → forecast
Measurements from many places are combined to work out the weather ahead
High and low pressure
high → sinking air → clear / low → rising air → cloudy, rain
Wind blows from high pressure towards low pressure
🎯 Key points
①A thermometer measures temperature, a wind vane the direction the wind comes from, a rain gauge rainfall and a hygrometer humidity
②High humidity makes clouds form easily, and thick clouds bring rain
③In a high, air sinks and it is usually clear
④In a low, air rises and it is cloudy or rainy
⑤Wind blows from high to low pressure, and the bigger the difference, the stronger it blows

Examples and Unit Test

Example 1
The arrowhead of a wind vane points east. What is the name of the wind blowing now?
1
The head of a wind vane's arrow points to where the wind is coming from.
2
The head points east, so the wind is blowing from east to west. A wind is named after the direction it comes from, so this is an east wind.
▸ An east wind (a wind blowing from the east)
Winds are named for where they come from, not where they go. Calling it a west wind because it heads west would be wrong.
Example 2
Which tends to bring clear weather, high pressure or low pressure? And which way does the wind blow between them?
1
In a high, sinking air breaks up the clouds, so the weather is usually clear.
2
Wind blows from the high, where the pressure is greater, towards the low, where it is smaller.
▸ High pressure tends to be clear, and the wind blows from high to low pressure.
In the picture above, a bigger pressure difference packs the isobars closer and thickens the wind arrow. The bigger the difference between two places, the stronger the wind.
Unit-test style
Which statement about weather and forecasting is correct?
①A hygrometer measures the direction the wind comes from.
②In a high, air sinks and the weather is usually clear.
③In a low, air sinks and the clouds break up.
④Wind blows from low pressure to high pressure.
⑤The higher the humidity, the harder it is for clouds to form.
▸ ② In a high, air sinks and the weather is usually clear.
1
In a high, sinking air breaks up the clouds, so the weather is usually clear.
2
A hygrometer measures humidity (①). In a low, air rises and clouds form (③). Wind blows from high to low pressure (④), and higher humidity makes clouds form more easily (⑤).
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