Choice between Synoptic and Numerical Forecasts
The D-day attack required perfect weather for success, so the commanders requested weather predictions using both of the available methods, to predict the perfect day within early June. The weather for May had been calm and the synoptic weather forecast predicted similar weather for early June, however numerical analysis showed an approaching storm and suggested the best day would be the 6th of June. The commanders accepted the prediction made by numerical analysis and thus D-day is forever, 6th of June 1944.
It was possible to make this numerical prediction due to the large amount of time between initiation of the forecast and the date that was being forecasted. This meant that forecasts for the next day using numerical methods were still not possible.
Dawn of Computers
John von Neumann, (one of the fathers of computer science) was the first person to think of using computers to generate a weather forecast; von Neumann and his
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This required the finite differences, which had been pioneered by Richardson. However, some of Richardson’s equations were still too complex for primitive computers. Charney developed the quasi-geostrophic approximation, which makes the assumption that there is an exact balance between the pressure gradient force and the Coriolis effect. This reduced several of the atmospheric equations into two equations with two variables. These pairs of equations were simple enough for early computers to solve. As an added benefit, these approximations filter out the fast moving small-waves, such as acoustic and gravity waves, which have little effect on the overall weather (these minor parameters are a part of the reason why Richardson struggled 30 years