I've been playing with this mod for a few hours now, and it seems like all the weather events are purely cosmetic? I have an idea for how to rework all the weather events to play into the game's lore. I saw that you're currently reworking how slugsomnia works, so I hope you take my hapless pleading from an obscure fan into consideration.

Firstly is the slugsomnia, or sleeping in. I think instead of you sleeping in from insomnia, it should instead be that the day cycle is slightly different from the Iterators' production cycle and sometimes goes out of sync. Downpour already has a Day/Night mechanic, so perhaps you could borrow from this. Usually, nightfall happens about a minute after the rain timer expires, only noticeable if you're above the clouds. If the rain cycle is mismatched with the day cycle, then this transition to nightfall would happen earlier in the cycle. Another mechanic from Downpour is nocturnal creatures. When the rain timer expires, most creatures return to their den, and nocturnal creatures emerge in some specific regions. With this mod's premature nightfall mechanic, every region's worldfile would be reworked to include night spawns (you can use The Exterior, Metropolis, and Outer Expanse as examples. Usually, it causes cyan lizards, big spiders, red spiders, and squidcadas to spawn, but outer expanse also causes monster kelp and white lizards to spawn.

Now onto actual weather events. I don't remember where, but I remember reading in one of the pearl dialogues that the Iterators' steam is the only thing preventing the surface of the world from freezing over because of the sun losing power over time. I'll be taking this into account when discussing weather spawn conditions. Oh also, it would be cool if custom regions that have their own weather effects are taken into consideration, but I won't bother you if they aren't. Stormy Coast experiences nonstop rain for most slugcats, so it shouldn't receive custom weather events, and a mod already exists to implement the lightning mechanic for this region. Arid Barrens has a sandstorm at the end of every cycle and is quite dry, so I think rain should be disabled in this region.

Rain: Personally, I think this should be tied to shelter failures. Experiencing a shelter failure should give a guaranteed chance to experience this low power rain for the rest of the cycle after the rain timer starts ticking. Of course, there can also be a small chance to experience rain outside of shelter failures if your shelter managed to withstand the weather. Every cycle in Rivulet's campaign would experience guaranteed rainfall, up until Pebbles' rarefaction cell is removed. Oh also, since this weather always appears after a shelter failure, it should force pre-cycle spawns to appear whenever this weather type spawns without an official shelter failure. (IE: monster kelp, salamander and eel lizards, etc)

Thunderstorm: This would probably have the same spawn conditions as rain, but be less common. Also, I think this should use the lightning mechanic from Watcher's version of Stormy Coast, which can stun or kill creatures directly in the blast. Thunderstorms would be more common in Rivulet's campaign. It would also feature pre-cycle spawns.

Heatwave: This would probably occur if the past few rain cycles have all been short, as the increased steam output would raise the temperatures too much. A heatwave causes you to become exhausted quicker. The effects of the heatwave dissipate over time when it occurs in longer cycles.

Fog: I can't exactly predict what would cause this to spawn normally, so this can probably just be left up to random chance, maybe higher chance in temperate climates (between hot and cold, determined by how long the previous cycles have been). Stormy Coast has a great fog effect in Spearmaster's variant you can use, in the Shrouded Coast version.

Snow: Snowfall would occur if the last few cycles have been longer than usual, as there's been less steam to heat the area up, resulting in the temperatures gradually declining. Snow would have a much higher chance of spawning in Rivulet's campaign after Pebbles' Rarefaction Cell has been removed, and would have a guaranteed chance of spawning after completing Moon's quest and entering Bitter Aerie. This does have a temperature mechanic, but it isn't enough to freeze you to death on short and medium length cycles. On longer cycles, the temperature slowly drops over time which can be hazardous in outdoor rooms. However, once the usual rain timer expires and the deadly rain begins to fall, the temperatures rapidly increase back to normal. Snowy weather also causes strawberry lizards to emerge outside of Saint's campaign, and causes centiwings to migrate further distances into nearby regions from Sky Islands.

Hail: Probably similar spawning conditions to snow, but less common. Also, this is probably the only weather type that has a chance of spawning in Saint's campaign. Being hit by hail can stun creatures briefly, but that's about it. Maybe this could be an opportunity to implement pre-cycle shelter failures in Saint's campaign, which would cause powerful hail weather to spawn during a shelter failure. And because it's a shelter failure, maybe you can get creative with having certain creatures spawn for Saint which usually don't spawn. Verde's World Fixes includes shelter failure spawns for Saint, so I guess you could just borrow those.

Distortion: honestly I have absolutely no idea what this is about. I guess make it a rare easter egg event. Explain it as a rare phenomenon involving the Void Sea when geological activity causes Void Fluid to rise near the surface, I guess

I'm sorry if this feels too demanding. I would love to implement a weather mod completely separately of this mod with these ideas, but I don't know how to code anything this complex in Rain World, so I'm limited to sharing my ideas with you because your mod inspired me with ideas.