The spell Control Weather has a radius of only 2 miles. But what if, for example, I create clouds and then create wind to push them out of the area? Do they vanish when reaching the edge, or do they move outside (and thereafter behave like natural clouds)?
Same question with the duration: if I create clouds, to they disappear immediately when the duration of spell ends, or dissipate naturally?
I'm in the camp that spells with duration and areas cannot suddenly be treated as instantaneous effects. Since Control Weather has an area of effect (2 miles radius or 3 miles if you are a druid) and a duration, if the weather you created within the area drifts outside the area it reverts to the actual weather, not the transmuted weather within the area. It's not like a Wall of Stone, which is is brought into existence by magic and is then just there - and could be broken up and moved. The weather change occurs only in the area, and only for the duration, and is subject to being dispelled, recognized as a running spell, and all other factors that involve ongoing spells.
What I wonder is that control weather seems to me, to be a "manipulation" spell like mage hand or telekinesis. The evidence is that it doesn't create weather patterns instantly, but it takes additional 10 minutes for the effects to manifest, and you can only create weather appropriate to the climate and season of the area you are in. So it may be like moving stuff around in atmosphere, rather than creating it out of nothing or out of something else. With manipulation spells, the object affected obviously maintains its position when the spell ends, and it doesn't stop abruptly if hurled out of the spell range.
Think also about things like rain puddles. Do they vanish when spell ends? Or, if I use it to water the crops, do they dry out again when the spell ends?
There's also a case in one of the Adventure Paths, where
Rain: The water stays IMO. You didn't create the water, the water is not magical. You manipulated the environment. It's kinda like if you cause a Tornado that kills a guy and flings him out of town. He doesn't come back to life or get put back where he was.. he's just dead and outside of the radius.
Duration: By the RAW; it looks like it completely dissipates the second the spell ends. By immersion or how i'd play it.. it'd probably stop doing whatever the bad thing is, and morph back into normal weather over the course of ten minutes. The ten minutes before hand as it starts up aren't your weather, but their your weather manifesting. I'd say the 10 minutes afterwards is the same way.
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I think in the case of the Hag Coven, it's probably just a super version of the spell that they didn't specify since it acts the same in other respects and is expected to be hand-waved. Honestly, I find it odd that there exists this notion that a GM should precisely emulate the exact rules and thus create a new spell, roll for it, have the hags casting it together, etc. etc. when in game terms it's really just a plot hook.
F.E. I started going through the motions of a (sort of) possessed book and all the stuff required to build it for real, then decided that all it really did was make it so it costed a bunch of fictional money that no one would pay for it anyway.
Another example: Super-powerful-artifact that destroys a specific Demon or something... do we really need to spell out exactly how it does it in game terms (other than damage, destruction, soul steal, w/e) instead of just saying "You did it!"? The result is the same with regard to the players and characters, except in one the GM wastes a whole bunch of time piecing together nonsense the players won't know about anyway.
TL,DR version: Using the rules and writing more rules for plot hooks or cool encounters isn't worth figuring out the precise details of.
That all said, the hag coven could be moving around, or if they used Enlarge Spell + Widen Spell they could have an 8 mile radius without moving. Funny enough, just using Familiar Spell would allow you to have a bird cast Control Weather for you.
Think of it this way your spell is manipulating the weather. Within your range you can shape the weather to what you like as prescribed by the spell. The energy from your spell is what is holding the clouds together and without the spell they quickly dissipate. Outside your range the normal weather conditions apply. So let’s say you use it to cause rain. It only rains in the two mile radius. Outside this radius it is not raining. The clouds do not extend beyond the two mile radius unless they were already present. Even if they were present they would not be raining unless it was already raining. So if the sky was clear and you caused it to rain there would be a 2 mile radius of clouds above the ground. It would look like an invisible wall was containing the clouds.
Once the rain falls it is no longer being controlled by the spell so it does what rain would normally do. For example of you caused rain to fall on a mountain it would run off even if the water goes outside the range of the spell. It would remain until it would normally evaporate.
Using something from an adventure path is not a good precedence. A lot of what happens in adventures falls under GM’s fiat.