Is yaw the southern why of saying you all?

You're close! "Yawl" is the Southern pronunciation of "you all".

Here's the breakdown:

* "You all" is a common phrase in many parts of the United States, particularly in the South.

* "Yawl" is the Southern dialect pronunciation of "you all", where the "ou" sound is shortened to a "aw" sound.

So, "yawl" is a contraction of "you all" that is prevalent in Southern American English.