I would like to create a mod so that it rains everywhere in-game. Does anyone know how i can go about creating this? Thanks.

Edit: Ignore me. Helps if i know what forum I am in before posting...

You could just go to the World->Regions menu, and change all the chances of rain to 100, and the chance of other weather types to 0.

Where do i find this menu?

Upper left hand corner in the CS.
You'll see 'World' between the 'View' and 'Character' tabs.

You don't, it's in the CS. However, it would also be an exceptionally bad idea; unless you want it to rain everywhere permanently.

A better idea would be to write a small global script, and do this for every region you want to effect:

modregion "bitter coast region", 0, 0, 0, 0, 100 ; for rain, or
modregion "bitter coast region", 0, 0, 0, 0, 0, 100 ; for thunderstorms

If you have bloodmoon, you can make that a startup script, and it will reset the weather parameters for you. The advantage here is that you don't create a very dirty mod, and it can be "undone" just as easily.

So just write that in notepad and place it in the morrowind folder?

No, you will need to use the CS.

Open the CS, hit the Folder (Data Files) button, and select the base files you want to modify. In this case, it will likely be at least Morrowind, and perhaps Tribunal and Bloodmoon if you have them. Since these are all masters, you won't be able to select an active file, so ignore that warning.

After that select Gameplay -> Edit Scripts. This will open a text editor called, imaginatively enough, Script Edit. Select Script -> New.

Once you can edit, type in:

begin noggins_rainy_daymodregion "Bitter Coast Region", 0, 0, 0, 0, 100modregion "Ascadian Isles Region", 0, 0, 0, 0, 100; fill this in with the rest of the regions - I'm too lazy to do it here...modregion "West Gash Region", 0, 0, 0, 0, 100stopscript noggins_rainy_dayend

Save that out - it will compile it, and assuming you didn't mistype anything, you should be back in the CS.

Next, if you are using bloodmoon, open GamePlay -> Edit Start Scripts. Add your script to the bottom of the list. If you are NOT using Bloodmoon, then you will need to attach it to something in the game world or use the console, and type "startscript noggins_rainy_day"

I believe you will need to pad out the zeros in the scripting to also cover the weather types that follow rain:

I know that will avoid any script errors due to expected params.

No argument on it being better, but generally as long as the probabilities add up to 100, the engine is fine with a partial list. It will barf if you don't exactly equal 100, though - either more or less.