Different types of weather effects such as snow and rain can be created using the fog emitter object that is available with the Ambitions expansion pack. While this does not give us full weather effects like an expanion pack would, it is fun to look at in the game or use for creating a machinima. Below you will find a tutorial showing the steps I used to create these effects in my game.

NOTE: More information can be found in the original topic that was posted in The Sims 3 Forums.

*Required Games
The Sims 3 Base Game The Sims 3 Ambitions EP

Start your game and load one of your Sim families. Go to Buy Mode. Open the cheat window by pressing Shift + Ctrl + C. Type in testingcheatsenabled true and press Enter. Next, type in buydebug and press Enter. You should see an objects menu appear. Click on the Misc. Objects tab and scroll down to the Fog Emitter.

Buy it and place it somewhere on the lawn. To activate the menu, press Shift + Ctrl and click on the object. Make sure that visual effects are enabled, then select Set Visual Effect.

In the box that pops up, type in the visual effect you would like to spawn using one of the codes below and click on the check mark.

Visual Effect Codes for Weather (a complete list can be found here)

rainheavydaytime
rainheavynighttime
rainlightdaytime
rainlightnighttime
raintorrentialdaytime
raintorrentialnighttime
snowfallingheavyday
snowfallingheavydaytime
snowfallingheavynight
snowfallingheavynighttime
snowfallinglightday
snowfallinglightdaytime
snowfallinglightnight
snowfallinglightnighttime

Go to Live Mode and you should now see the weather effect you entered. To change to a different type, press Shift + Ctrl and click on the fog emitter in Buy Mode. Select Reset Visual Effect > Set Visual Effect, then type in a new code.

Videos of the snow and rain weather effects that I have created can be found HERE.