I'm reliably getting different results about the max and min preps of geyser from discern and perc. VOI, another spell that changes preps day to night, seems to be working though. So far, it seems to be limited to geyser.

>discern geyser
The Geyser spell is unique to the Water Manipulation Book, as it deals with waters deep below the surface rather than those nearby or in the air. It is a targeted spell that draws superheated water up from below and directs it toward your foe. Mind that, in some places, even with a mastery of the water element, there may be insufficient passage for the blast to escape the depths.

This is a targeted spell, which must be TARGETed at a specific opponent. This spell does impact and fire damage. It can be cast on other adventurers and hostile creatures. It requires a minimum of three mana streams, and can expand to a maximum of ninety-six mana streams woven into it.

To begin to be able to cast this spell, you will need to reach the rank of a lowly novice. By the time you have mastered this spell, you will be ranked as a professional in your abilities as a caster. It requires the Targeted Magic skill to cast effectively.

This spell has no prerequisites. It will also cost one spell slot.

You think you could weave at least 31 mana streams into this spell.
Roundtime: 7 seconds.

>pre gey
Since you're not feeding enough power into the spell pattern to make it coherent, you quickly work your way to the minimum required.
You trace a careful sigil in the air, shaping the pattern of the Geyser spell.
>perc
You have fully prepared the Geyser spell at four mana.
Roundtime: 8 sec.

>pre gey 200
Since you're attempting to feed more power into the spell pattern than it is capable of utilizing, you quickly work your way down to its maximal potential.
You feel intense strain as you try to manipulate the mana streams to form this pattern, and you are not certain that you will have enough mental stamina to complete it.
You trace a careful sigil in the air, shaping the pattern of the Geyser spell.
>perc
You have fully prepared the Geyser spell at one hundred two mana.
Roundtime: 7 sec.

I thought WM spells got weather or environmental based modifiers to spell costs, which would be reflected in what you're seeing?

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Adding nothing to the conversation since 1834.

It's not just the randomness, I can get different levels of success, but the prep numbers stay the same.

It now appears to be an indoor/outdoor thing:

>discern foi
The Fortress of Ice spell must be woven with at least 28 mana streams, and can contain up to 98.

You don't think you are able to cast this spell.
Roundtime: 12 seconds.
>out
You lumber out.
[The Crossing, Scorpion Lane]
You also see a brilliantly painted sign displayed prominently in front of the Artificer's Shop.
Obvious paths: north, east, south, west.
>discern foi
The Fortress of Ice spell must be woven with at least 26 mana streams, and can contain up to 96.

You don't think you are able to cast this spell.
Roundtime: 13 seconds.

I guess that makes sense- geyser is hot so you'd need more mana when its cold at night.
The others being harder to cast in the warm day, since they're cold.

I'd think Geyser would be harder indoors though.

If anything it looks like the minimal day indoor prep for geyser is too low.

And VOI night outdoor cast caps too high. Assuming its just as easy to cast inside as outside.

Nice data.
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An agonizing pain fills you as you feel your tongue turn to powder in your mouth! Through a haze of uncertainty and loss, you realize that something you just said was very wrong.