I would want to see the entire picture before cropping to do a good job of it...
I messed around a bit with what you had posted but didn't really improve it. I'm imagining that there is more of the cloud off to the right in the full version?
If possible, I'd crop it so that the center of the illuminated storm clould (actually, looking again, the darkest part of the storm cloud is what I perceive as the center) was centered in the left 3rd of the pic, rather then centered in the center of the pic. With what you have posted, removing the some of the image on the left leaves the center of the storm in an awkward position, stuck somewhere between 1/3 and half from the left.
I can't come up with a top/bottom position without having more to the right.
After spending some time with it, this is what my eye does: Goes right to dark spot in center of storm, browses around at illuminated storm clouds, drifts off to the right, returns to the far left, goes to top. My mind has a hard time returning to the storm and I lose interest in it.
Taking what you posted, and cropping it in the following manner causes my eye to look at the center of the storm, browses the illuminated clouds, drift to the right, and always return to the center of the storm to rinse and repeat. My interest is actually held longer and I focus more on the interesting clouds and shadows in them.
Thanks for posting this, it has given me a really fun opportunity to really examine how I react to framing of a scene.