Salve Fratres!
Considering the fact that Christmas is almost upon us I decided it's time a good time to add a couple of things to this collective letter to st. Nicholas. Maybe someday in the future, he'll grant us our wishes
Just as other people suggested, adding weather conditions would definitely be interesting. I think they could be introduced in a similar fashion to the map terrain profiles like Agricultural or Hilly. And just like those map types, they could come with their own terrain types unique to the season/weather as well as some additional effects on the performance of certain units.
How I see it it could look like this:
I. We could choose from an array of weather types or leave it at random. Those weather types would be:
1) Warm - this would default weather in random battles, representing the clear sunny spring/summer/early autumn day
2) Warm (Rain) - this would represent a rain light enough that commanders did not decide to postpone a confrontation waiting for better weather (battles during heavy rain or storms rarely ever happen), yet it would still inflict a slight shooting penalty to bows, crossbows, and firearms and artillery only leaving javelins unaffected.
3) Winter - winter battles and sieges weren't uncommon in the Early Modern Era, especially in Eastern Europe. Shotting penalty for crossbows, no penalty for muskets/arquebuses.
4) Winter (Snowfall) - a winter map with a snowfall, applies a slight penalty to firearms and a more serious penalty to crossbows.
5) Warm/Winter (Fog) - instead of applying a boring shooting penalty I think fog should simply reduce every units' line of sight. It would make Fog battles more interesting (pun intended)
II. Now with some of those weather types, there could be added terrain types that are unique only to those weather conditions. For example:
1) Winter and Winter (Snowfall) could have:
a) Deep snow - the equivalent of Rough Terrain. Costs more AP to travel through and disorders Cavalry, Heavy and Mixed foot.
b) Snowdrift - an obstacle similar to hedges we know from the English Civil War module. They would provide 10%/34% cover (moved/unmoved) and protection from rear and flank charges.
c) Frozen Stream - it would either replace all streams (regular and deep ones) or just be added as the third type of stream available only on winter maps. The frozen stream could cost more ap to cross than regular terrain but wouldn't disorder any troops and maybe it wouldn't count as closed terrain at all.
d) (optional) Frozen Rivers and Lakes. Again either replacing regular ones or simply a chance of spawning this type instead of the regular ones. Unlike the normal Rivers/Lakes the frozen variety is a passable terrain. I guess it is up to discussion if it should be passable for all units or maybe some like Gendarmes, Tercios/Keils and artillery should be excluded.
e) (optional) Frozen Marsh - offers 10% cover if unmoved but no longer disorders. Regular marshes shouldn't be replaced but rather be mixed with them to represent ice holes that can be often found in marshes due to the heat produced by decaying organic matter.
2. Warm (Rain), I don't think this weather condition should come with any unique terrain types, since Rough Ground can already represent muddy ground well enough. My only suggestion could be that in Random Map if the weather condition is set to Warm (Rain) there should be a higher chance of spawning deep streams instead of regular ones and a higher chance of spawning marshes representing wet meadows. Hmm, you know what, maybe Wet Meadows could function as a separate terrain type offering the same penalties as marshes but without the cover bonus?
III. Optional stuff:
1) Additional weather condition available only in the Editor called Warm (Rained) that would imply that... yeah you guessed it, it was raining before the battle, either night before or earlier the same day. It would allow applying a custom penalty to either both or one of the sides of the battle implying they did a poor job at keeping their strings/gunpowder from getting wet. We could also decide on the severity of the penalty from 10 to 24% (independent for both sides). We could also decide if all units are affected or just the artillery. I think that would be useful for recreating certain historical battles.
IV. Explanation and summary: I thought I should offer some explanation for some of the proposals. I think that default penalties for shooting during rain and snowfall should be rather small as soldiers usually weren't complete idiots and did a good job of protecting their bowstrings or gunpowder from getting wet. So my suggestion is that the penalty for snowing and rain should be about 10% to represent additional time and care being put be soldiers to protect their weapons from being affected by the weather and to represent a higher chance for misfires in case of firearms and artillery.
Crossbows are an exception though since I suggest they should suffer a penalty from snowfall and an additional penalty just from the cold weather. I suggested so because metal prods (bows) of the late heavy crossbows are prone to crack in low temperatures. On top of that cranequins or windlasses can freeze or malfunction in another way in low temperatures.
Another thing you might notice is that I didn't include more extreme weather conditions like Snow Storms and Heavy Rains. That's because historically speaking such weather would prevent the battle from starting or force both sides to disengage.
P.S. I apologize if someone else already made a similar suggestion in this thread or a similar one.
P.S.2 This would also fit nicely in FoG 2 Medieval since Middle Ages contrary to popular belief also saw a decent amount of winter warfare, especially in Central and Eastern Europe since Mongols/Tatars often launched their raids during winter. Not to mention the famous effects of rain in the Battle of Crécy.