To see it, you must first enable the clouds layer, and then zoom in to a location where it’s raining or snowing. Google Earth displays rain and snow only in certain parts of North America and Europe; to see where exactly the new feature is available, enable the radar layer.
The weather simulation adds another layer of coolness to the already mesmerizing Google Earth application. Since it displays rain and snow in real time, the feature can actually be useful as a precise visualization of what weather is like in a certain place. It may, however, render all of those weather-related chats you have with friends and relatives over the phone even more meaningless.
Unfortunately, there’s no word on when this feature might be enabled in other parts of the world.