Learning to read Pressure and other Weather Charts

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KTtom
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Learning to read Pressure and other Weather Charts

Post #1 by KTtom » Sun Dec 21, 2008 8:24 am

The main charts posted are H500 charts such as below. We won't worry too much about the colours at the moment (not 100% sure myself) they are temperature related but rather atmosphere temperatures as opposed to surface temperatures were interested in.

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High Pressure

The above chart is a H500 pressure chart. Areas of high pressure are usually in yellow and identified by 'H'. The white lines on the charts are Isobars. There lines link up areas of equal pressure. In the case of high pressure the highest pressure is in the centre of the cell and falls away with each line.
The winds will always follow the Isobar lines and with areas of high pressure will rotate clockwise around it. The closer the white lines the stronger the winds.

If you trace the lines back you can get an idea of whether the temperature will be warm or cold. If you use the example above you can see that the lines although circulating the area of high pressure pass through Russia before they pass over the UK. Obviously in Winter Russia is very cold and therefore cold air will filter to the UK. During winter the two areas we want to see high pressure is Scandinavia (as above) and also Greenland (which is fairly rare these days) to avect really cold air over this country.


Low Pressure

Areas of low pressure are usually in darker colours such as below, these are identified by 'T' (Trough). Areas of low pressure are associated with unsettled conditions. The Isobars surrounding these low pressure's, just like high pressure indicate areas of equal pressure with the lowest pressure in the center of the cell and rising as the lines move away.
The important difference when tracing the lines back to get an idea of wind sorce, is that the winds circulate the low pressures anti-clockwise
From the example below, the winds can be traced back to the Arctic and northern Scandinavia prior to arriving at the UK. Therefore it will be cold.

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During Winter months the ideal areas to have low pressures are to the north east of the UK to bring in northerly winds (above) or to the south of the UK to introduce easterly winds (below).


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Combining low pressure to the south and high pressure to the north in winter can bring bitter condition.[/quote][/quote]
Last edited by KTtom on Mon Dec 22, 2008 7:19 am, edited 1 time in total.

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