Its been raining constantly where I live, and in many areas of the USA there is flooding. So am not sure its the mantra causing rain, but am sure it can get us off the bodily concept! :-) I do agree, however, that the Maha Mantra "can" cause it to rain, but unless you look up the weather ahead of time and 'then' chant, 'then' see what happens, its more likely suppose to happen anyway. Or you could go back if they have archives and see what kind of weather was predicted for that day you chanted and it rained out. However, these things are not so important. That we learn to love and serve Krishna, is. :-)

YS,
Prtha dd

P.S. I also think Ancient makes a good point that chanting Hare Krishna increases our overall sensitivity or awareness regarding what goes on around us.