This mod is now end-of-life and replaced by my new much larger and better RAID Weathers mod.

This mod has many tweaks and fixes that generally improve how ELFX Weathers looks and plays in Skyrim SE.
It also optimises ELFX Weathers for users (like me) who do not like heavy eye-adaptation or bloom-blur effects, and do not like the washed out look caused by Skyrim SE's godrays. There are also large performance improvements to the custom rain weathers.

This mod has had some optimisations for sneak detection balance, using my experience as a detection mod author. This means the amount of darkness you see on screen more reliably indicates how easily NPCs can search for enemies there. Most other weather/lighting mods have serious problems where darkness does not reliably affect how easy it is to hide. A more detailed explanation of this topic is available on my Realistic AI Detection mod page.

Stock ELFX Weathers was already one of the best weather mods in terms of sneak balance, but this mod takes that further. Tedious precise adjustments were made to sunlight scale, sunlight, ambient, DALC, and other weather data points.

ENB users: While I don't use ENB myself, the changes and improved consistency of this mod should mean it works well with some presets.
However, any ENB presets that make some environments darker should be avoided if you want the best sneak detection balance.

This mod does not include night sky textures, so I highly recommend you get HLP Night Sky ("medium" version). It goes well with ELFX Weathers.

Main Features:
Removed virtually all laggy eye-adaptation "hdr" effects from ELFX weathers.
Improved sneak light level balance and consistency for many weathers.
Reduced Bloom and Blur effects for most pleasant and cloudy weathers, providing a sharper clearer look.
Improved visual appearance of all rain types (the screenshots do not show this well), and improved intensity of some rains that were barely visible.
Fixed the low FPS of some ELFX custom rains (by optimising rain texture and particle settings). VRAM usage lowered by ~400MB !
Fixed many instances of poorly set brightness/color for grass, trees, sky, clouds, distant fog, tint, horizon seams, etc
Increased chance of sunny weather (closer to vanilla skyrim chance), while lowering chance of dull overcast weather. Rain/snow chance unaffected.
Increased brightness of many cloudy weather types to be more reasonable (less gloomy).

Other Visual Tweaks:
Improved consistency of sun glare for various clear weathers (some had a lot while others had none strangely)
Increased bloom and blur for some of the heavy rain/snow/fog weathers that oddly lacked those effects.
A few weathers that had virtually no clouds at all during the day now have a few small ones.
Many other tweaks. See the changelog for more details.

Compatibility:
Not compatible with other weather mods.

Installation:
Install the ELFX suite (including ELFX Weathers)
Make sure to get the right ELFX patches as well: ELFX SMIM fps patch, ELFX Fixes, ELFX - Exteriors Fixes , and ELFX Dwemer Floor Footsteps Fix
Assorted Mesh Fixes is also recommended as it fixes some mesh bugs that are very noticeable in heavy ELFX fog weather (load before ELFX).
Install this "ELFX Weathers" mod, ensuring it replaces the default ELFX Weathers plugin
If you use "ELFX Enhancer" or "ELFX - Hardcore", put ELFX Weathers below them in your load order! (LOOT often auto-sorts it wrong)
Install Imaginator (and it's optional MCM download), set it's brightness to about +40 (this is different from Skyrim's default brightness slider)
            Adjust Imaginator tint settings to your preference. My settings are shown in the last screenshot (but your monitor colors may differ a bit).
INI tweaks required for this mod to look like the screenshots:
Skyrim.ini
[Weather]
fSunBaseSize=210     (optional, this makes the sun smaller, and stops it from shining through small solid objects)
fSunGlareSize=250    (optional, this reduces sun glare as shown in the screenshots, if the stock ELFX amount seems excessive to you)

skyrimprefs.ini
[Display]
bVolumetricLightingEnable=0    (this disables godrays to remove the washed-out look they cause in skyrim)

(nice) Side Effects of this setup:
Using Imaginator to increase weather brightness will also increase indoor brightness significantly. This means it does a similar thing to the "ELFX Enhancer Brighter Lights" mod here on nexus.

Credits:
this patch work by Olivier Doorenbos
based on the Skyrim Legendary Edition weather module from "Enhanced Lighs and FX" by anamorfus (permission given)