Because the atmosphere
is chaotic, uncertainties, no matter how small, would eventually overwhelm any
calculations and defeat the accuracy of the forecast. This principle is sometimes called the "Butterfly Effect."
In terms of weather forecasts, the "Butterfly Effect" refers to the
idea that whether or not a butterfly flaps its wings in a certain part of the
world can make the difference in whether or not a storm arises one year later
on the other side of the world. Because of the "Butterfly Effect," it
is now accepted that weather forecasts can be accurate only in the short-term,
and that long-term forecasts, even made with the most sophisticated computer
methods imaginable, will always be no better than guesses.