If you center the Cloudkill spell on yourself, does the fog expand outward from you on subsequent turns?

Question

The description of the cloudkill spell says (emphasis mine):

You create a 20-­foot-­radius sphere of poisonous, yellow‑green fog centered on a point you choose within range. The fog spreads around corners. It lasts for the duration or until strong wind disperses the fog, ending the spell. Its area is heavily obscured.

[...]

The fog moves 10 feet away from you at the start of each of your turns, rolling along the surface of the ground. The vapors, being heavier than air, sink to the lowest level of the land, even pouring down openings.

If you center the cloudkill spell on yourself, does the cloud expand outward on subsequent turns, since it moves "away from you"? Or would it stay as a single unit and roll off in a direction of your choice?

Answer 1

"Moves", not "Expands"

This is a circumstance the rules don't cover perfectly (presumably because the designers didn't consider a character being stupid enough to cast this on themselves) so officially you will need to ask your DM, but here is how I would rule it.

The important part of the spell's text is highlighted below:

The fog moves 10 feet away from you at the start of each of your turns [...]

The key word here is "moves", implying that the entire cloud moves together. The direction it moves in is somewhat arbitrary. Either you can decide your your DM will decide for you.

Allowing it to expand increases the power of the spell

To rule the other way and rule that the cloud can expand outwards in a ring from its point of origin makes it a more powerful spell. I'm not going to get into the math, but if the cloud expands outward each round, it also increases in area. Increasing the area of effect of a spell increases its power level.