Most likely someone somewhere in the area had a monster scorch-up in their kitchen. Or at one of the restaurants. You can get bubbles of trapped cooler air in the valleys and the warm that is coming in rides over the top and pushes everything down.. Groveton gets the same sort of Mystery Smells in the early fall.

I'm on in Portsmouth now, and for the last few days there's been a wandering burnt sweet soap smell which more often than not, is coming from the Schiller power plant. God save you when one of the kids fucks up a batch of coffee at the coffee roasters nearby, and burns it. It's Downwind Death.

When the thermals trap air bubbles, that is when things get really interesting as far as odors.