On a Mac, it's usually not RAM that is the issue but video memory. I don't see any indication of you flying through storms in the log, so I think you're just exhausting video memory. That's very common on Macs as they typically don't have much of it. And when X-Plane crashes due to running out of video memory, it typically does so in this fashion where it just stops without writing any diagnostic information into the log first.
If you're flying through custom scenery, that's likely consuming quite a bit of it. Disabling HDR can also help. Or, you can lower SkyMaxx Pro's cloud draw area setting. The new volumetric clouds in SkyMaxx Pro 5 also use more video memory than the non-volumetric options do.