Just my geeky perspective, but let us look at what seem to be the facts:
1) These patterns APPEAR to have color, which implies something optical. The Prandtl-Glauert Singularity just produces vapor. Such vapor sometimes does produce color, but also tends to appear in a conical shape. Prandtl also predicts a radius much, much smaller than what we see in the photo.
2) P-G concerns the separation and re-attachment of airflow at high Reynolds numbers (which need not be transonic), but the patterns we're seeing do not seem to result from detached flow, especially when you consider the asymmetrical ring around the nose. In addition to the evident color, please also note that this ring around the nose seems to be almost actually TWO rings. The second one, sharper and less cloudy, looks like it is just forming/becoming visible.
3) Just assuming for argument's sake that there is some kind of P-G effect, what about the shapes we're seeing behind the left wing and ahead of the right-wing pods? Seems like a totally different kind of effect, and not at all related to the classic "N" shape shockwave that is predicted and well-observed. Also, we know that transonic waves will creep up from behind the trailing edge, but this airplane is flying much too slowly for that. At approximately 5,000 feet, this airplane is doing probably 0.2 Mach. We sometimes see condensation developing below and behind extended flaps at such speeds, but this aircraft is clean and we know that it was a cold day (-11C), so ice crystal formation (sublimation) is more likely than condensation.
4) We should also consider what is NOT. Maybe the aircraft in the photo is nowhere near the actual phenomena. Looking at it, the Boeing appears to be above the bow shape, yet far below the trailing edge shape. The pod shapes seem to vague to judge, but all three shapes seem to have a similar intensity and coloration.
5) Also missing are the wingtip vortices often visible in high-humidity conditions. If we were dealing with a P-G effect, then we would expect to see tight vortices coming off the wingtips.
6) Related to 4, maybe it is flying THROUGH some kind of ring-shaped vortex created by a factory or a local explosion of some kind (these are well-documented), but the photographer claims to have seen the phenomenon actually repeat itself, which is why he said he raised his camera in the first place. If the effect repeated itself, the aircraft was not flying through an existing vortex. UNLESS it, by some massive coincidence, managed to re-enter or remain in wake turbulence from a preceeding aircraft. Could be, and I've seen it happen.
7) The bow shape resembles a parhelic circle. These usually form at a 22 degree angle between the observer and the object, which is plausible here, but how to explain the non-circular shapes ahead of the right wing and behind the left one? Again, potentially two different effects.
Just a little comida for thought,
m.