WHAT THIS MOD CONTAIN/DOES:
This is a reworked (not only just ported) plugin which makes possible to see original LE Climates of Tamriel weathers on SSE with additional fixes improvements from Mangaclub made especially for CoT. This mod is based on Vivid Clouds and Fogs - Vanilla and Climates of Tamriel, not on original CoT LE.
"Wait! isn't CoT SE already exists on Nexus?" - of course it does but SE version has been recreated from scratch and brings colors closer to vanilla SSE rather than original LE. The difference is COSMIC.

List of features changes made inside provided plugin:

Provides exact classic colors of the Climates of Tamriel from Legendary edition which looks completely different from not only CoT SE, and any other SSE weather mod. The color concept is a photo realism, but those who prefer vivid/fantasy colors can easily get those using ENB (please read further).
Suitable to everyone who want a maximum variety of weathers ever seen for Skyrim (almost 500 weather variations), but without seasons (for example, it means that there will be no snow every day during the calendar winter).
Technically, this patch is a replacer for main plugin of Climates of Tamriel LE, which combines main .esm file, original CoT plugins for DLCs Dawnguard and Dragonborn, and also data from Vivid Clouds and Fogs - Vanilla and Climates of Tamriel. All in one.
Carries new weathers probability, cloud speed and far horizons blur removal from the Vivid Clouds and Fogs patch.
The performance will cost you zero FPS loss. So don't worry about the performance at all.
Vanilla weathers (exact classic colors too) will appear between the CoT weathers sometimes, that increases the variety even more.

DEMO (without ENB)

DISACLAMER

I am not the author of the Climates of Tamriel for Legendary Edition. Under the permission of JJC71 and Mangaclub (Vivid Clouds and Fogs LE) I made a patch which makes old classic CoT to work on SSE in exact condition as it was initially, plus impovements added by the Vivid Clouds and Fogs mod for the original CoT. Please show your attitude to the original mods creators and endorse their mods.
This mod is provided as is. I just shared what I did.
Some patches and further modifications will follow, when I will have time for it.

INSTALLATION STEPS:

Text version of the installation steps (any mod manager):

1. Download Climates Of Tamriel V (LE) (CoT LE).

2. Start CoT LE archive installation though the mod manager and choose manual instead of FOMOD, then untick all contents and choose only ClimatesOfTamriel.bsa) to unpack it as a mod.
Alternatively you can create mod folder for CoT LE (name it as you want) in mods folder and manually unpack only ClimatesOfTamriel.bsa file from the downloaded CoT LE archive into new created mod folder.

3.1. Unpack the contents of .bsa file into CoT LE mod folder and delete .bsa after that. To do that you can use mod manager's built in BSA unpacker (MO2 has it) or use an external tool, like this one or this one.

3.2. Delete unpacked meshes folder or allow this patch to replace it during step 2.

4. Install CoT Legendary SSE as usual mod and place the activated plugin somewhere higher in your load order.

Note about load order: some lighting mods may alter the "Image Space" data or weather sounds, so you will get non-original colors in some places. In this case it's up to you, what mod must dominate. Some patches will be released a bit later. You can send the the patch and I will publish it here, or you can create a mod page for your patch.

5. This step is OPTIONAL. Use it only if you want to replace beautiful CoT clouds by the no less beautiful Vivid clouds:

5.1. Install Vivid Clouds and Fogs by selecting only one option called Vivid Clouds Climates of Tamriel (in the main section or a half resolution version if you have low amount of VRAM).
Warning: don't enable any other checkboxes unless you are experienced user and know you are doing (for example want additional textures for steam). Just don't forget to delete any .esp plugins after installation, if they appear in Vivid Clouds and Fogs directory, because they are in Form 43 and will conflict with my mod.

WHAT ABOUT VOLUMETRIC LIGHTING?

Very simple - volumetric lighting was suppressed by adding the parameters of VOLI data from Skyrim Legendary Weathers to each CoT weather. So all CoT Legendary weathers was ported correctly. I recommend to disable the volumetric lighting by setting the parameter in SkyrimPrefs.ini
[Display] bVolumetricLightingEnable=0

Q: Do I loose graphics quality without the Volumetric Lighting?
A: No, quite the opposite. The classic picture given by the Climates of Tamriel Legendary is much much better than SSE weathers with Volumetric Lighting. Besides, many people found these volumetric godrays very annoying, because they appearing everywhere, even when they shouldn't.
If you using ENB, you may still get a nicely working godrays while the game volumetric lighting is disabled via INI setting. Just find the ENB preset which provides godrays shader.

As you may know, ENB for SSE does not contain [MIST] settings as it was in ENB for LE, so a disabled volumetric lighting in CoT Legendary can be easily compensated by installing Volumetric Mists.
You don't need this mod if you don't like hazy far horizons and want to see all the way up to the farthest mountains.

Of course, whole this thing does not mean that in CoT Legendary there are not fogs in far horizons. The Volumetric Fogs is more like an amplifier for existing fogs and also it adds the fogs in clear weathers, where CoT Legendary does not have them.

SUITABLE ENB/RESHADE PRESETS:

Reshare preset you may try, if ENB is too heavy for your system: TrueShade Redux.

Now about ENB.
If you not an experienced user, I will gladly tell you some useful info on ENB presents. There are two main categories of ENB presets out there:
1. ENB's made for a specific weather mod as a strict requirement. that's because these ENB's using locational weather system, which determines individual parameters for each type of weather, and even location (dungeons/caves, specific places).
2. Weather independent (universal) ENB's. These presets are not tethered to a specific weather mod and can match many of them out of the box, but some parameters still may need to be adjusted a bit. But overall it's a good alternative if you using a weather mod, on which there are no specific ENB yet.

Currently there are no specific ENB created for this mod, but you can use weather independent ENB presets:

The Truth ENB - matches a photo realism style of CoT Legendary at 100%. No adjustments needed, unless you want to make nights darker/brighter using ENB settings.
Ljoss ENB - provides vivid (saturated) fantasy image, so CoT weathers will become very colorful. May need some adjustments of ENB settings to suit personal taste.

CREDITS / GRATITUDE:

Huge thanks to JJC71 for Climates Of Tamriel V (LE)
Huge thanks to Mangaclub for Vivid Clouds and Fogs - Vanilla and Climates of Tamriel (LE)

Huge thanks to omega2008 for Skyrim Legendary Weathers

Climates of Tamriel Legendary with Vivid Clouds