During earlier discussion of this topic, Tom KQ5S told us about the VOACAP propagation modeling presented on the K6TU web site. The link I provided here gives an overview of what's needed to run the model program on the web site.
A little web searching today about "do-it-yourself" VOACAP usage brought the following article from 2004:
Two other search results raised my awareness of the VOACAP dependence on sunspot data and how it is defined and published:My searching today reminded me that the VOACAP capability is also a plug-in built into the 4nec2 antenna modeling software that I use. I've seen it in one of the program menus, but have not digested the documentation enough to use it.