Term 2 – Week 3 – Weather

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Snow that fell over the weekend

This week we learnt how to read weather maps and come up with our own forecasts. It was quite timely since we were due to get the first snow of the year that weekend – and yes we sure did get snow!

weather

Example of a weather map for the South Island

Some good websites for weather forecasts are MetService or MetVuw.

The maps show areas of high pressure or low pressure. The lines on a weather map are isobars that connect areas of equal pressure. When isobars are close together it means there will be strong wind.

lo

High pressure (over 1000 hPa) means weather will generally be calmer and will have clear skies. The higher the pressure number the slower the system will be moving. The wind will travel anticlockwise around a high (clockwise in the Northern Hemisphere). A ridge is a section of higher pressure extending from a high pressure system. Ridges give better than expected conditions. Highs move towards lows and will look like they are following them across the map. In summer weather should be sunny and warm and winter will be cool and frosty.

Low pressure is where all the drama happens. Clouds, rain, cyclones (940 hPa), hurricanes (800 hPa) and tornadoes (500 hPa). Air (filled with water vapour) is rising and expanding, when it reaches the dew point the water vapour condenses, forming clouds. Lows move clockwise. A trough is a section of lower pressure extending from the low, bringing worse than expected weather.

clouds

Types of clouds

There are so many different types of clouds. The lowest being fog and highest are cirrus. Cirrus are the very high looking, wispy clouds. They can indicate that a change in the weather is coming in the next 24 hours.

Cumulonimbus clouds are massive clouds that go right up to the top of the troposphere. They can bring hail, lightning, tornadoes and flash flooding. They form when there has been strong heating at ground surface or from a cold front slamming into warmer air.

Fronts are a boundary between warmer and cooler air. They don’t like to mix and cause trouble in the form of clouds and rain.

fronts

Although a warm front sounds like it would be nice, it’s not! All fronts bring worse weather. Stationary fronts can cause lots of rain and flooding. Yuck!

I’m crossing my fingers for lots more high pressure systems coming my way, although if I can’t have that, I will take the snow 🙂

Last week’s weather:

weather

 

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