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FORECAST WINDS FOR MODELLERS

by Geoff Graham

http://www.wetterzentrale.de

If you go to the url shown above you will be able to view charts which indicate the surface winds in forecast steps which are 12 hours apart. These range from 12 hrs ahead through to 144 hrs ahead (6 days). Do not be put off by the fact that the charts at first look complicated. They are not. Add the url to your favourites now as you might have a job remembering where it was when you next want to use it.

Once you arrive at the site, you will see the following screen:

On that "front page" there are in any case some nice charts. Bottom left is the U.K. meteorological office surface analysis, which is useful. On the right there are "metric" forecast charts out to different periods ahead. By metric I mean that the isobars are 5mb intervals whilst British practice is 4mb intervals. How to use them? Well, for the layman, colours depict temperature and isobars if packed mean windy. If wide open, that means generally, though not always, not windy.

To proceed, click on the words "Top Karten" over on the left, as highlighted with the red box above. This will take you to the following screen:

You will see this scroll-down menu at the top left of the screen; click on AVN and you will go to this view:

Go to the large scroll down AVN - Europa chart at the top of the screen and highlighted in red above, and scroll down to the bottom of the chart.

From the 10m Wind row of the chart, click on the period you wish to consider. If you want to see the winds on which the forecasts were based, or initialised, then click on Analyse. If you want to know what it will be like the day after tomorrow then click on 48hr and so on.

Having clicked on your selected forecast period, you will see this chart displayed:

This image is shown here as a thumbnail, so that you can view it full size by clicking on it.

1. The winds are 10M (10 metre) winds. This simply means that they are forecast for a level 10 metres above ground level which is the international standard for measuring what we call "surface wind". So these are OUR winds and ideal as a source of forecasts for our flying day planning.

2. Before you can run a computer forecast the machine has to be "initialised" using measured weather data, in our case winds. The initialisation time is shown top left as for example Init: Sun,06MAY2001 00Z. This means that the input winds were measured at midnight Greenwich Meantime (that’s the Z bit) on the 6th May. Meteorologists call that time zero hours on the 6th hence the 06th 00Z. So a 12 hour forecast will be for midday on the 7th.

3. The time when the forecast will actually be found to be right or wrong (in Met Man terms "valid") is shown as say Valid Sun062001 12Z.

4. What do the arrows mean? Well, the shaft shows the direction from which the wind is blowing. The "feathers" indicate 10 knots (about 11mph) for a full feather and 05 knots for half a feather. Therefore, two and a half feathers mean 25 knots or too windy for us!

5. Colours are used to show "fields" of wind strength and for our purpose it has to be blue really. Deep blue is perfect unless of course you are a sloper or PSS guy.

The AVN chart is still displayed at the top of this screen, so you can select other forecast periods if you wish. 

Be patient and spend a little time playing around with these charts and you will soon discover that they are very handy for forward planning. On the whole I would expect these forecast models to be pretty accurate especially out to two days ahead.

Finally, if you want much more detail, then go to the BBC weather pages and on those you will be able to select regional maps for the UK and select wind forecasts for 12 or 24 hours ahead. The wind is depicted differently. The direction is shown by an arrow and the strength by the thickness of the arrow and how closely they are packed together. These BBC charts are in very much closer detail than the Top Karten charts which are really designed for professional aviators and meteorologists and the like. That does not stop us using them to our modelling advantage though.

It goes without saying that you also need to check weather or not it will be chucking it down with rain as well as calm!

I found this article of Geoff's absolutely fascinating. The step-by-step procedure to get to the web site which I expanded to some degree may sound a bit lengthy as you read it, but it is really only a question of a few mouse clicks. When I first looked at the big chart, though, it took me a bit of time to spot the actual map of Europe faintly drawn in the background! Note also that if you select the bottom line of the AVN chart (10m Wind (Mitteleur.) the view shifts to the east, to give a view covering central Europe.