Google Maps now has a weather layer!
If you select the weather layer on Google Maps you can view the current temperature and weather conditions for where ever you are. You can also see the current cloud coverage for the whole world.
If you want a weather forecast for a location you can also click on the weather icon for a particular city. An info window will then open with a detailed summary of current humidity and wind conditions, as well as a forecast for the next four days.
Via: Official Google Blog