dba_afish said:
as I'm writing this, I've made my way several miles northwest and am now situated, as far as I can tell, directly under the glowing patch of sky.

there is still no fully determinable terrestrial source.

Perhaps a spotlight. Road work or some festival ground can have those focused intense bright lights, and one of them could be pointed or reflected up onto the clouds. With the light at even a slight angle, the source can be a fair distance away on the ground from where it seems to be on the clouds.

it was fairly large and stationary, much larger than most spotlights. and, from my experience, with high-power lights like that you can usually see the, like, profile of the beam all the way light refracting off of small particles or the moisture in the air or whatever.

the only explanation I can come up with is that it was just garden variety suburban light pollution, just a strangely concentrated, very blue instance of it, caused by some group of nearby buildings. the biggest candidate is the medical centre which would make sense for the timing, since they'd obviously stay open past midnight.