Frostfell Prodigy( Frostburn, p. 48)
You gain additional bonus spells in cold regions.
In cold areas (temperature at or below 40Â° F), the ability score used to determine how many bonus spells you may prepare or cast is treated as if it were 2 higher than its actual score. If you enter an area with a warmer temperature and remain in this area for longer than 1 minute, the bonus spells granted by this feat are lost until you can regain them. In areas of extreme cold (below -20Â° F), the ability score is treated as if it were 4 higher than its actual score for purposes of determining how many bonus spells you can prepare or cast.