STTH3010W thermal resistivity to ambient

[DBiro.1]

I'm currently measuring the power loss of a 3 phase rectifier comprised of STTH3010W diodes.  I have my preliminary results obtained by measuring the voltage drop and current through an individual diode on my oscilloscope.  I'm just looking now to verify my results with the temperature data I've collected.  Do anyone have a good estimate on the Rth(j-a) or Rth(c-a) rating of the STTH3010W or even maybe just the DO-247 package?

[MasterT]

Data sheet has this:

[DBiro.1]

I believe the data sheet only has the thermal resistivity from junction to case, Rth(j-c).  I'm trying to find the relationship to the ambient air as well, Rth(j-a) or simply Rth(c-a).  Since it would be based on the package I'm wondering if this information has been gathered from any of the other similar packages or if anyone has a good estimation of this.

[AScha.3]

from STTH1512  ds :