How accurate are long term weather forecasts?

On the Autumn Equinox, here in Britain our minds start to turn to the prospect of snow. And, of course, the Daily Express runs their annual dramatic headline of the worst winter in years, but how good are weather forecasts? The Met Office has recently said that four day forecasts are now just as accurate as the one day forecasts in the mid 1980s. But as far as long term, 30 day forecasts are concerned we may well be waiting a while. Because the atmosphere is so chaotic, tiny observational errors occur all the time. Tiny they may well be, but they're the kind of errors which make a huge distance!