I think I would like to see the top a little lighter. The dark color on the top makes it top heavy. Another problem I feel is that the image does not really have a centre of interest which makes the eyes wander throught the image without a feeling. If it was of intent to show the vastness of the sky then there has to be a scale somehow, a clue to the vastness so that a viewe can understand the statement. The other option is to figure out some pattern in the clouds which I am not able to see here (maybe it is there and it is my problem). This image qualifies well with the challenge topic but has to be well focused as to what is the statement regarding sky that you want to make in this pic. Best of luck for future.