I don't think the foreground in this photograph is doing anything. It would be better to wait for more interesting weather (as already suggested) and get the tree with some dark, moody clouds. Perhaps the tree could be low in the frame to increase a feeling of oppression.
Just my opinion. Thanks for sharing.
This shot would be a winner if you reshot it right before a storm! That would be more dramatic. Also a little less foreground, although keep some, because it will help draw the eyes to the tree
Perhaps keep the ammount of foreground but shoot from alower level, thus moving the skyline up the picture. Try a red filter to bring out the clouds in the sky a little, or even better, a graduated red so the foreground is unaffected, heightening the contrast further. it also looks like arable crops. Why not wait unril the harvest has gone and the land ploughed and resown. You can get some interesting patterns from the tilling/seeding(?) gear the tractor drags.
It seems like there is too much gray. but I like the idea and the foreground really leads your eye to the tree. If there was a more interesting sky it would be almost perfect for me.