Hi,
Some 10 years ago the "Times" checked that point and found that the weather prediction is only a bit more than a toss of a coin (If my memory serves me well the figure was 54%).  However since than time a great progress has been made, and with all sattelite maps I believe that the weather prediction is far better.  I don't have the exact figures but I guess that it should be somewhere between 80% to 90% (which means pretty much accurate).
Beast regards,