Nice work! maybe the middle cloud a little too blury and the big building near the guy have too much orange i dont thing the light of the explosion woul be on that side. Maybe destroy some building near the explosion.
It's a very good work.
But it doesn't show the disastrous destruction such a bomb actually can have or had.
I personally would enlarge the bomb to double size and make it much much brighter. And the edges of the bubble should be brighter then the sky.