A large amount of weather information is readily available. However, normal forecasts are often too generalised for us and there is nothing quite like a synoptic chart to give an idea of what is going on. Synoptics generated in the UK Met. Office are readily available on the internet from the German weather office (www.wetterzentrale.de) and other sites. Quite a selection are available and it helps to know a little about how they are generated and what times they appear. Each chart has a title at the top which might read something like 'ASXX MSLP ANALYSIS For 0000 UTC 04 MAY 2002' or 'FSXX 24H MSLP FORECAST Valid 1200 UTC 05 MAY 2002'. Initially these may seem little more helpful than the inscriptions in Tutenkhamun's tomb, but they are really not so bad once you understand a few key points.

Each chart is generated from information collected at weather stations around the world every six hours, 0000 (midnight), 0600, 1200 and 1800, often referred to as time 'T'. These times are given in UTC, the same as Greenwich Mean Time which we use in Britain in winter and one hour behind British Summer Time. The information is then transmitted to Bracknell from all over the world and processed to give a synoptic showing the state at the time of the readings. This is a mammoth undertaking and even using some of the most powerful computers in the world it takes some time for the charts to be produced. The first chart normally appears about 3 hours after the readings are taken at about 4pm BST for the 1200 chart. This chart has the designation ASXX MSLP. 'AS' stands for 'Analysis Surface' meaning it shows conditions at the surface of the earth. I find it easier to remember 'A' for 'Actual' readings. MSLP is Mean (average) Sea Level Pressure.

We are really interested in forecasts rather than actual synoptics. A chart given as 'T + 24' it is a forecast of conditions expected in 24 hours from the time the readings were taken. This chart becomes available about 7 hours after the readings are taken and has the designation 'FSXX' (Forecast Surface). The accuracy of these forecasts has improved considerably over the years and the 24 hour forecast is usually very good. Longer forcasts, T + 36, 48, 60, 72 ,96 and 120 hours, are of decreasing accuracy so it is important to check the time of the readings from which a forecast is made.

We can examine forecasts from as far ahead as we like but as a potential flying day approaches we become more focussed on the conditions expected around mid-day. Because of the time taken to generate them, the chart which shows the period we are interested in most accurately is the 24 hour forcast made from data at mid-day the day before, FSXX 24H. This is available from about 6pm the day before to about midnight so we will have to either save this as a file or print it if we wish it to be available on the day itself. I often take a print onto the hill with me.

We know that the closer together isobars are the windier it is. To get an actual wind strength from a synoptic we use the 'Geostrophic Wind Scale' at the top left of the chart as follows:

1) Take a small piece of paper and place it so that one edge lies across the isobars over the area you are interested in at right angles to them.

2) On the edge of the paper mark the points at which two adjacent isobars cross them.

3) From the chart check the latitude of the area you are interested in. Britain lies between the latitude circles centred on the north pole marked 50 and 60 (this is the angle in degrees north of the equator).

4) Place the marked edge of the paper horizontally on the geostrophic wind scale with the left mark matching the vertical left edge of the scale.

5) The numbers 40, 50, 60 and 70 on the left of the wind scale represent the latitude. Move the paper up or down so that the upper edge is aligned with the latitude you determined in step (3).

6) Read the wind from the numbers at the ends of the curved lines running from the top to the bottom of the scale. If your mark on the edge of the paper falls between the lines then make an estimate of the value.

7) The wind speed in the example above is about 20 Knots. This is only going to be approximate but there are two correction factors which are worth applying, particularly as we fly relatively slow aircraft.

a) Add 15% to get miles per hour (making the example 23 mph) or 80% to get kilometers per hour (36 kph in the example).

b) Add a further 5% if the isobars depict an area of high pressure and subtract 5% if they depict an area of low pressure. If the example was of part of a high pressure system then the wind would be about 24 mph or 38 kph.

Lastly, a small point that has bothered me from time to time. With some settings web browsers do not always recognise when a chart has been updated and show the last one you have downloaded instead. If this happens and you don't want to tinker with the settings then use the 'Refresh' key to ensure you get the latest chart. With delays of 5 hours between data collection and the 24 hour forecast making sure you get the right chart at the right time is crucial.

The above is only a little of what can be done with synoptics using a limited amount of the information available. More can be extracted from them if you have the time and patience but equally there are other web sites such as Weatherjack and the UK wind map listed on the BHPA web site which give good information in an easily understood form. Nevertheless, if you can begin to understand the relation between what is shown on synoptics and conditions in your local area then you may just get away on that extra cross country flight that you might not have otherwise managed.