Can anyone recommend a web weather service which offers a forecast for a
particular day and location?

I envisage something like the following:

For long-term forecasts it would rely upon historical data.
As the date approached, it would begin to rely upon forecasts based upon
the current situation.
As the date became closer and closer, the estimated accuracy would be
displayed as a rising percentage until, on the day itself, it would read
90% accuracy. It would perhaps appear thusly:

12:00h, August 2nd, 2007, Greenwich.
Wind: 10 knots
Temperatu 12 degrees C
Rain: Heavy
Certainty: 24%

Each day, it would be updated with the best estimate, and the certainty
would increase slightly.

What would be great would be if the above were available in xml to allow
web widgets to be made for desktop users. People could put their
birthday in there, or their wedding day, or Christmas day... I hope you
get the idea.

--
-Toby
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