Shiloh was fought on april 6th and 7th so the weather was not all that warm, even in the south. plus I've seen some re-enactments there and there were plenty of greatcoats. your right about stones river, that's another good one. man I can't wait for these new sets to come out!!!!!!!!!!!!!!!

Fredericksburg was fought in December so there are lots of great paintings of soldiers in winter outfits. Don Troiani did a wonderful painting of the Irish Brigade charging up Marye's Heights at Fredericksburg. Link:

https://www.google.com/search?hl=en&site=imghp&tbm=isch&source=hp&biw=1920&bih=963&q=fredericksburg+battle&oq=fredericksburg+battle&gs_l=img.3..0l6j0i5i30k1j0i8i30k1l3.1828.10904.0.11535.21.17.0.4.4.0.166.1846.1j16.17.0....0...1ac.1.64.img..0.21.1883...0i30k1.5sZTMdpCV0w#imgrc=5AWHT9_5j7gyCM%3A

The weather at Shiloh was unseasonably warm in the Spring of 1862.