I also thought of the particle emitter method. (Actually it uses at least two, because you're bouncing one off the ground with a wide angle for the base shockwave while another one goes upwards.) But it's tricky as heck to get just right because of all the variables.  Involves having no or low negative gravity, just the right blur effect setting over an applied alpha image (because having actual clouds as a rendered particle object will kill your CPU and take way too long), low particle mass and high air friction, and some things involving particle lifespan in the shader (color and glow channels) to make the clouds look firey and violent... To be honest though, the particle emitter way is likely much more useful for animations where you want to see the cloud rising into the sky than doing something quick for a still image. (And it can look impressive if you manage to get it right, but it's not that easy.)

Gotta admit though, Mark's way is genius for achieving the effect quickly in still pics. No tweaking 500 times and guessing what shape the resulting particle cloud will take.

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Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
Also feel free to browse my freebies at ShareCG.
There might be something worth downloading.