You spew a thick cloud of dense black smoke that forms a 5-foot-diameter, 10-foot-high cylinder centred on you that lasts until the start of your next turn. The smoke heavily obscures its area. When you cast the spell, you can choose whether the cloud remains in the location where you cast it or if it moves with you, centred on you.   When you reach higher levels, the size of the cloud you can create with this spell increases. When you reach 5th level, the cloud has a maximum diameter and height of 15 feet; at 11th level this increases to 25 feet; and at 17th level this increases to 40 feet. You choose how big the cloud is in each dimension up to this maximum each time that you cast it.