Been saying this for years mate. You ground the sprayers and suddenly the natural atmospheric systems do what they actually want to do instead of being suppressed. Hot air just builds and builds with nothing interfering with the jet stream patterns.
I noticed similar out here in Norfolk last summer actually - there was a two week window where the trails just stopped completely and we had this bizarre persistent high pressure that wouldnt budge. Checked the flight radar and it wasn't like commercial flights had stopped, just the high altitude back-and-forth stuff was gone.
Not saying I have it all figured out but the correlation is hard to ignore once you start actually paying attention to the skies on a daily basis. Most people dont look up. Like ever.
Anyone got the specific dates for the Phoenix grounding? Would be worth mapping it against pressure system data from the same period and seeing if theres a pattern across multiple locations.