toxicspirit said:
Wouldn't 'line of effect' come into play in that scenario?
It does, but if the trees are lightly obscured, does the wizard have LOE or not? It's a good question. I would say that in reality (a bad model, I know) she has LOE to some spaces, but clearly the trees will block other spaces... it seems like simply treating it as cover for all targets of the area burst spell works OK to simulate that, but it's not RAW, and I am trying (and failing!) to stick to RAW whenever possible.
I could mess with a Perception check at -5 (see DMG 61), but what is the DC to see a monster in plain sight? I would not think it very high, so that's not really useful.
DMG 43 says "A tree between a creature and the center of a fireball helps protect that creature from the blast, not a tree between the creature and wizard casting the spell." I disagree with this though: if that tree is large enough to prevent the wizard from landing that fireball in the correct spot...
Actually this raises a very important question. A fireball in 3.5E is a tiny ball of fire that explodes when it reaches its destination, so it has to travel from your fingertips to the correct space. In 4E, do you just "think" a fireball "8 squares forward and 2 squares left" and have it magically appear there? In that case, I guess it is a Line of Sight question, and as long as you can see the square at all, you can think up the fireball there?