Wet and Cold is a staple in my load order since I can remember. I just recently came back to modding but this time built my load order around the awesome Seasons of Skyrim mod and realized that both mods are not that immersive together - for example winter gear is equipped all winter long when your Skyrim is snowy.

Since there is no patch or other mod to fix this I decided to do it myself and here we are. 



This mod is intended to be used with the Wet and Cold - Gear version by Oz3. This edit of Wet and Cold removes the visual effects and go home feature (wich is integrated in many follower frameworks or AI overhauls anyways) and is overall more lightweight than good old Wet and Cold. For the visual effects I highly recommend the much more modern R.A.S.S..
I also integrated in my mod a patch made by Flip777 (look in the discussion for details about it on Wet and Cold - Gear's modpage) which all in all together results in the most lightweight version of Wet and Cold you can get at the moment without a rewrite of the original mod or developing a complete new one from scratch. 

This is the first version of this mod to see, if I've overlooked any bugs or larger issues. It runs quite stable on my load order with over 1500 mods with some minor hickups from time to time when heavily using coc console command (see the troubleshooting section). So please report any weird behavior you encounter! 



I created two flavors of this integration patch, a lite or simple version and a more complex version.

'Lite' means in the winter months of Seasons of Skyrim everyone (minus the Nords and exceptions handled via the SPID config files of Wet and Cold - Gear like blacksmiths) will equip winter gear. For the rest of the year, rain gear and cold gear (I didn't make any changes to ash gear with the exception of the winter months) will be equipped depending if it is snowing or raining. That's it. 

The more complex flavor takes seasonal transitions into consideration to show, that the temperature is gradually rising but not everyone is ditching his or her cold gear in the first month of spring - but, depending on the region the NPC is located, maybe change the cold gear for a more lightweight hood and cloak (aka the rain gear) in these transitional months.

This results into the following distribution: 
 
All seasons are the same as in Seasons of Skyrim, this is a list of the corresponding GameMonth (the global CK variable, also used for the console command set gamemonth to #), Skyrim's calendar month and in which seasons the month belongs:
 

The regions above are the same as in the Creation Club Survival mode; I personally play also with Sunhelm enabled and all works fine. 




This sounds complex and heavy but in reality it is quite light on the performance (not more than Wet and Cold - Gear), because I mainly got it done with native CK Condition Functions, which means a better performance instead of using Papyrus scripts. There are a quest, spells and several effects with scripts attached used to get this whole functionality working - but these are lightweight scripts (just 5 lines of code and no additional cloaking spells!) which will only trigger the global variables which will then be processed natively as conditions in engine. These scripts will also fire only on region or game month change.
I've also used a little trick: when I'm at Winterhold in First Seed I don't need the NPCs in Whiterun to equip their transitional cloths (rain gear), so all these more complex behaviors are dependent on the player location.


Just install my mod after all dependencies and let it overwrite everything!
You can see if my mod is installed correctly if the 'mode' option in Wet and Cold's MCM on the 'Wet' page, right side,  upper half has disappeared and you see directly the NPC options at the top.

Required mods (in this order): 
Wet and Cold SE
Wet and Cold alternative freezing fix
Wet and Cold - Gear (with it's dependency SPID)
My Mod
Seasons of Skyrim - well not technically required but why else would you need this patch?

Highly recommended mods: 
Seasonal Landscapes - Unfrozen for the best effect that temperatures rise over the year, even in the really cold regions
Seasonal Weathers Framework to set that in the summer months no snow is falling - otherwise the NPC will equip 
Time Flies SE and Dynamic Timescales SE to experience all the Seasons in a normal Skyrim run without editing the game months 



As mentioned sometimes the equipment of the gear when it is raining or snowing could be bugged; this is an old bug which I could not resolve fully. But it has an easy solution: just enter an interior cell and go outside again, everyone should already equip or has equipped the needed gear. 

Also notice: weather transitions in Skyrim happen gradually, which means you could encounter first snowflakes or raindrops but no one is equipping the gear right away. As said, Skyrim handles this as transition with a value between 0 and 1 and the equipment of the needed gear is handled when isSnowing or isRaining = 1. In my testing this was barely noticeable but there are some rare cases in which the transition takes some time and either the NPCs equipped it before you could visibly see snow or rain or with a slight delay. But nothing dramatic or immersion breaking.

To see if the mod is working correct you can set the game month with the console (set gamemonth to #) to either 11, 0 or 1 and everyone should equip cold gear (if not, enter an interior cell and got outside again; everyone should equip it now).
For the more complex flavors go to any of the cold or freezing regions (I often use Whiterun and Winterhold exteriors as test region) and set the game month to any of the early/late spring or autumn (2, 10) or mid spring/autumn months (3, 9). 
The NPCs should equip the right gear right away. In this alpha version I also exposed the global variables to you magic effect menu. If all is working fine you should see an effect appearing with the name 'Check if in a Cold region', 'Check if in a Cold region in the warmer months' and so on (see images, the first 2 show how it should look like in early spring or late autumn in freezing and cold region, image 3 and 4 for mid spring and autumn).