WeatherSync

This plugin keeps the weather on your server synchronized with the real-world weather in a location you specify. It does this by connecting to weather underground every few minutes (configurable; 5 minutes by default) and parsing the weather. This means if it's raining outside, it will be raining in minecraft. This is also true of thunderstorms.

You will want to configure it before you try to use it; otherwise it will synchronize with the weather in San Francisco, California. (Used for testing.)

Download

See more and get help on the Bukkit forums.