Upgliding 'open o'

[Gordon, Matthew J.]

Kind of a technical question:

Can someone tell me about the conditioning of upgliding diphthongal variants of  'open o'  ( the vowel of caught, dawn, etc.) heard in the South (Midlands)? Do they occur in all environments? Kurath and McDavid (1961) note they're more common before /g/ and the velarized /l/ of 'salt'. I'm particularly interested in possible differences between following stops and nasals (e.g., caught vs. dawn).

thanks