let's not be too hasty....before blaming it on the heat(which it very well may be),did you install carbon fibre rods?
because i had the exact same thing happen a while back from not having the carbon rods deepo enough,they were pushing the fretboard up in the middle,and it cracked...
it could also happen if your truss rod was not installed to the right depth.
from here
http://projectguitar.ibforums.com/index.php?showtopic=4599
all it takes is a fraction of a mm to do it
and by the way,the only thing that can be done in this case is to remove the board,rout the rods deeper,and reinstall a new fretboard
edit....i just saw your pics and i realize you bought rthe neck blank premade...so yeah,it's probably the furnace