In a "mountains and valleys" type area, there is a very large fire (say, an acre or two) that generates a lot of smoke. Where would the wind be strong enough and constant enough in this type of geographical area to blow enough of the smoke away so that people could still breathe and not pass out from smoke inhalation? Would a heavy rain or thunderstorm stop the wind from lessening the smoke?
An acre or two fire is tiny. The recent fire on Mt. Graham in Arizona burned 48,443 acres over the course of approximately 3 weeks.
As a general rule, a large fire will create its own updraft, pulling the smoke higher up into the air. Any areas which can be well ventilated from the outside by this updraft will generally clear smoke. If you have a corner where the outside air can't get to, it could fill with smoke.
Rain is rather good at pulling smoke particulates out of the air, so I would expect a heavy rain to help far more than it would hurt. It also helps put out the fire!