Augmented Flames, raises damage by 25% at first rank or 50% at second rank. The damage values are compounded the closer your targets are, so the damage break down is as follows:
This is by far the most expensive spell to cast in terms of magicka, limiting its practical uses. However, if you can obtain 100% Fortify Destruction, this downside will be eliminated.
Firestorm also hits airborne targets, such as Dragons, though they have to be hovering within 100 feet (the furthest the spell can reach) in order to have any effect.
This spell will hit everything around you, including allies, so you should only use it if you're traveling alone or with followers who are marked essential.
If you have Dragonborn installed, you can embark on the quest The Winds of Change; one of the three rewards is the ability to not damage your follower while in combat (though your follower can still die by other means, such as stray arrows or explosions caused by other enemies while in bleedout), making the Fire Storm 100% follower-friendly. [verification needed — see talk page]