Media for Snow/Fog/Rain Guidelines?

Snow/Fog/Rain Guidelines?

I am planning on deploying a test 802.11g point-to-point system to hopefully replace an old coax network. I am wondering what the impact can be from rain, fog and snow. Where I am located gets all three and in abundance and variety. A full deployment on site would consist eventually of multiple point-to-multipoint and a handful of point-to-point links with the distances ranging from a few hundred feet to almost a mile. The longest run would have to contend with other issues too such as NLOS due to a tree that we can't quite get high enough to shoot over.

I have read a few posts on the subject that suggest rain and snow don't have quite as much impact as fog but I am wondering if anyone can point me in the direction of quantified impact? I'm intending to make sure that the links have more than enough "power" but I was wondering how much would be an appropriate margin for the various types of weather events that can impact 2.4GHz signals. Also, what impact does light foliage cause? Can it be "blasted through" or is some other solution more appropriate?

Thank you, James Thompson