Regarding rain attenuation:

It turns out that water molecules are particularly susceptible to having their internal vibrations enhanced by microwave radiation. This is how microwave ovens work: the microwave energy is converted to heat by the water molecules in the food. (The real explanation involves quantum physics.) A radio receiver in the microwave range will have difficulty receiving signals in the presence of rain, since the microwave signals will (to a small degree) be used to heat the rain. The extent to which this happens is calculable, and whether the received signal is affected or not is determined by the fade margin built into the system. Thus, all other things being equal, a larger dish, or any antenna with higher gain, will have a greater fade margin and will be less susceptible to rain fades. Of course, with GPS and Neverlost, since you're stuck with what they give you, it either works or it doesn't.