Smoke was not used as a screen in the manner it would later be used during WWI and WWII. It was a visibility problem in battles depending on the weather. If there was little wind and high humidity the smoke would hug the ground reducing visibility. I have read several accounts of officers attempting to peer under the smoke to see the enemy and in my readings on the bombardment at Gettysburg before Picket's Charge several officers commented on their inability to determine the effects of their fire due to the smoke.
You can create weather lines that will do nothing but affect visibility, for more information on this check out the ACWGC Engineering page on PDT files http://www.acwgc.org/ACWCO_Engineering/
However the problem is there is no way to base this on the amount of combat currently taking place so you could end up with full visibility during lots of shooting and reduced visibility when there is no combat occurring.
Any reduction in visibility based on the amount of firing taking place would require programming changes in the main program.
Gen. Ken Miller
1/2/VI
AoS
