It adds a more realistic weather system than the standard rain and snow.
It also adds a series of storms ranging from hail and lightning to tornados and hurricanes. The storms will spawn randomly as rain and snow do but they will also spawn better in certain areas. Rain clouds will gather over areas with more water for example.
All mods in the list blow are available in the Minecraft Modinstaller (click here)... Alternatively we offer you mods here as a ZIP File you can install manually: