How Much Damage Can Control Weather Do?

[Schadenfreuda]

The text of the spell in the PHb suggests that it can create natural lightning and even tornados (during spring, the very least), which would suggest fairly apocalyptic power given an area of over twelve square miles and an environment of mostly wooden buildings or otherwise crude constructions. But it's frustratingly unclear on the finer details, except that you can't make lightning strike exactly where you want. Does anyone know if there are any published clarifications anywhere? Or maybe suggestions from in-game experience on how to run it?

[Paragon]

You can check the DMG p93 for the details on what different weather grade can do (some damage included). The three environmental books might have some other weathers to add (sandstorms, frostfells or waterstorms)

[rel]

I'd rule it isn't much good for dealing with a CR appropriate enemy. Nor is it guaranteed to kill anyone specific or destroy anything specific.
However, if you target something sufficiently large, you will deal sufficient damage to destroy it or render it nonfunctional.

Examples of suitable targets are:
- Large piles of unprotected supplies such as caravans, baggage trains and seedy warehouse districts.
- poorly built or badly positioned settlements and camps
- large groups of low level creatures such as armies or convoys

I'd rule anything like that effectively destroyed unless it's unusually resilient, local conditions are highly uncooperative or high level opposition exists. If the PC's are aiming to destroy something very specific (e.g. the warehouse of Shady Steve who sold us out) then I'd use a simple percentage roll to see if said target was destroyed.

Ultimately, barring something unusual like a scroll or incantation, the spellcaster can just keep casting the spell every day until it sticks. So if the Archdruid has decided to personally register a complaint about your sacred grove logging operation, the only way your shiny new lumber-jacking camp is not getting washed out into the ocean is if you send your own band of high level murder hobos to engage in some 'public relations'.

[Chronos]

If it's tornadoes you want, then the lower-level spell Control Winds is much better. With Control Weather, you can make tornadoes in the area, but then they just do what tornadoes do, which is wander around randomly. Whatever they do hit will be devastated, unless it's very strong, but they'll just randomly miss lots of things.

With Control Winds, though, you can make tornado-force winds throughout the very large area, and as an added bonus, you can make them blow in whatever direction you want. And you can also designate a circular safe zone of whatever size you want, if there's something you don't want to hit.