I did my "Definition of terms" in the other thread, but here it is again:
Low/weak: Light the fire, purify the water in your canteen. Both simple and local.
Moderate: Fireball, lightning bolt, Black Channels, permanent walls. Powerful perhaps, but still very local. Raising the dead is at the upper end of this.
Powerful/High: Hurricane, rain of fire, plague. Things that are both complex/powerful and on a large scale.