Deme, 6 months ago (edited 6 months ago)

This is the 22° halo. A Corona is an entirely different phenomenon caused by diffraction and interference of light around tiny water or ice particles, or other such particles of similar size. Halos on the other hand are formed by refraction. Here’s another great resource about coronae (and pretty much every other atmospheric optical phenomenon out there).

You’re correct about halo phenomena being caused by ice crystals. As such, they are most often observed when there’s Cirrostratus in the sky, and that in turn is often the result of an incoming warm front. The Cirrostratus may start to thicken into Altostratus and Nimbostratus, so overcast and rainy would be the safest bet.