Weather is a map property added on the Christmas Update for the first available weather effect, Snow
Weather currently serves no actual gameplay contributions other than it's function and its cosmetic appeal. Weather works as if it was an actual object. Weather effects do not enter into areas enclosed by solid blocks. However it can go through all platforms. Notice that it still runs in the BackGround if it has got solid tiles above in some cases, like when there are Window Tiles.
The following is a list of current Weather Effects. All weather effects do not go through solid blocks, weather effects do go through platforms and Objects.
Added during the Somewhat Merry Christmas update in Pre-Alpha 1.1.5 it falls gently as if it were real snow. Does not leave Snow Blocks on the ground, they must be added manually over the other blocks.
Added during the Ch-Ch-Ch-Changes Update in Pre-Alpha 1.2.0, falls like a normal rainy day.