In this section I would like to give you some basic weather knowledge. Below I have included information relating the Cloud types, the basics to reading a weather map and how a twister can be formed.

Clouds

Rarely in this part of the world do we have a day without a puffy white cloud somewhere in the sky. Clouds are nothing more than water vapour that has condensed and has clumped together. To explain why clouds are white we must first understand why the sky is blue. It will help, trust me.

As light travels down to the earth the blue light of the visible spectrum is scattered by the nitrogen in the atmosphere and other air molecules. As this blue light scatters between molecule and molecule the light appears to be coming from all directions giving us a "blue" sky.

When clouds form, the water droplets are much larger than the moleclues in the atmosphere. These droplets scatter and reflect all the light, thus giving the clouds a white colour. Darker clouds are just thicker and the light does not penetrate as well, giving them the grey/black colour.

Cloud types

Clouds are classified into 10 main clouds types.

High level clouds - approx. 5-13kms above sea level.

Cirrus - very high, wispy and white

Cirrocumulus - very high, white and small

Cirrostratus - very high, wispy and white. These are the clouds that form the halos aroung the sun or moon

Medium level clouds - approx. 2-7kms above sea level.

Altocumulus - white or light grey, rippled, or in small rolls or cells

Altostratus - white or grey, layers, the sun can be only faintly seen through it

Low level clouds - the base of the cloud is below 3kms (though some of these clouds can reach 19kms

Stratus - low, white or grey, no rain

Stratocumulus - low, grey or whitish, sheets or patches of cloud in the form of rolls,lumps or rounded masses

Cumulus - low, white, fluffy, heaped

Cumulonimbus - low to high, vertical, dark, rain

Nimbostratus - low, dark, heavy rain or even snow

The Basics of Reading a Weather Map

How to Read a Weather Map is what Meteorologists are trained to do, but even their predictions are rarely accurate over a three to four day period. Most of the time Computers are used to "model" the weather, helping the meteorologists tell us whether the weekend would be good for a BBQ or maybe it's better to go to the movies.

If we all lived on the flat and in the middle of the ocean, the weather would be even easier to predict. But in all places the weather is also affected by the geography of the land and you must take this into account when forecasting. The majority of the South Island of New Zealand is divided by the Southern Alps. These mountains can hold up a huge amount of weather that predominantly spreads from the West across the Tasman Sea. The West Coast is renowned for wet weather, where the East Coast can be at times, dry and warm.

This aside, below I have listed some basic features you will recognise on an Isobaric Map.

Cold Front - Usually a band of rain followed by showers.

Warm Front - A mass of warmer, sometimes moist, air.

Low Pressure Area - An area of low pressure. The isobars are closer together which means the winds will be stronger.	High Pressure Area - An area of high pressure. The isobars are further apart which indicates lighter winds and more settled weather.

Air circulates around these systems and "generally" follows the Isobars ("iso" = equal, "bar" = pressure), clockwise around the Lows and counter-clockwise around the Highs. As mentioned above, the tighter the "lines" are the stronger the winds will be, but this is also affected by how close you are to the Equator. If the isobars are same distance between each other over the bottom of the South Island and the same distance between each other over the top of the North Island, the winds nearer the Equator will be a lot stronger.

So with this in mind, when looking at these maps you should be able to tell which way the wind is likely to blow and roughly how strong it will be.