Yes, the arthropodan societies have advanced the science and lore of meteorology beyond anything known to us mere primates.
There may be something to read in the size of the anthills, but I would suppose they're larger because there are more ants, not because those ants are smarter.
As for the steepness of the anthill slopes, it depends only upon the angle of repose of the stuff the anthills are made of. If they're steeper, it's probably because the dirt is wetter, which in turn could be either (1) because the weather has been wetter, or (2) because, there being more ants, they had to dig deeper and pulled out wetter soil.
But what do I know? I'm a mere
Homo Sapiens and surely can't match the intellect of myrmicine or formicine critters like
Solenopsis Invicta and his cousins.
Anyway, I think your observations show only that nobody has been poisoning the darned things.
Here's an interesting article about them.