What do /a/ and /O/ merge to?

[Douglas G. Wilson]

I'm an originally Detroit/Chicago type now living in Pittsburgh.

Typical Pittsburgh "don" and "dawn" sound identical, and both of them sound
to me like my "dawn" (with what I would write /O/).

[Pittsburgh "down" sounds about like my "don" (with what I would write
/a/). I have mistakenly heard Pittsburgh "power" as "par" and "pound" as
"pond"; Pittsburghers and immigrants to the area joke about "dahntahn" =
"downtown" etc. sometimes.]

-- Doug Wilson