How can I make this explosion animation look better?

This is supposed to look like a grenade exploding. Because the size of the explosion will end up being much larger than 32x32, I plan to start multiple animations at a single point and then move them all away from that point in different directions.

Perhaps there's a better technique to what I mentioned above, but here's my rationale/requirements: The explosion radius needs to be a specific size, but that specific size may change over time for balancing reasons. I'm trying to avoid redrawing the animation every time I change the size of the explosion radius.