Although Yahoo Weather has a metric mode, it is, unfortunately, incomplete. The textual forecast still uses things like "29F" and "15 to 25 mph". Since this is not very useful for the rest of us, I wrote a Greasemonkey script which fixes the problem. It even tries to do something sensible when encountering things like "in the upper 30s".

So "Low 29F. Winds E at 15 to 25 mph" gets converted into "Low -2C. Winds E at 24 to 40 kph", while "Temps nearly steady in the low 30s" becomes "Temps nearly steady around 0C".

A reasonably good URL to test this script would be: http://weather.yahoo.com/forecast/DAXX0009_c.html.

The latest version of the script can be found here.