Thanks for the responses.
Rich Kurtin wrote this interesting article on the Fanaticus site for DBA, some of which I think would be interesting to convert to FOG, such as the fog visibility ranges and a possible - POA for shot in the rain:
http://www.fanaticus.org/DBA/variants/weather.html

:D It's also true that commanders tried to have battles in the most favourable conditiona and terrain, so both sides might avoid it if conditions were unfavorable. Reading other wargames sites, including weather conditions can bog down a game (pun intended). However, I read all these battle accounts...

Thanks. I'd better come up with some then!

Sorry if I missed this in the rulebook, but are weather effects shown anywhere?

i was reading about the french wars of religion, and noted that the arquebusiers couldn't fire in damp conditions.