## Comment Re:Really ? (Score 3, Informative) 176

When quoting Arnold I have been a little incorrect, since five figures of precision in the measurement of physical variables actually give you a two months forecast. But I studied this about thirty years ago...

If you want to estimate the error, if n is the number of months of the forecast and eps is the measurement precision, the error is given by:

10^(2.5n) times epsilon. As you can see the error rapidly increases, although the formula I transcribed from Arnold's textbook is quite rough (toroidal Earth, steady flux and negligible viscosity). Not a bad approximation for estimating trade winds flux, however.

People at MET probably took care of the propagation of numerical errors in the calculation, by increasing the grid density and maybe setting up a system capable of working with quadruple precision. However the problem again is the needed precision of input data, that increases exponentially with the time forecasted.

If you want to estimate the error, if n is the number of months of the forecast and eps is the measurement precision, the error is given by:

10^(2.5n) times epsilon. As you can see the error rapidly increases, although the formula I transcribed from Arnold's textbook is quite rough (toroidal Earth, steady flux and negligible viscosity). Not a bad approximation for estimating trade winds flux, however.

People at MET probably took care of the propagation of numerical errors in the calculation, by increasing the grid density and maybe setting up a system capable of working with quadruple precision. However the problem again is the needed precision of input data, that increases exponentially with the time forecasted.