When it rains the "rain" goes through Forge Multipart blocks.
Also after a storm the memory usage goes to 95% then Minecraft freezes then it goes down to 80% ish then back up to 95% then Minecraft freezes then it goes down to 80% ish and goes back up

I don't know if this will work, but these should fix many issues with the particles that the mod uses.

Head into the pause menu and go to the Weather2 EZ Config area. Head into the Advanced settings area via the Advanced button on the bottom.

In the first page, find the option called "useEntityRenderHookForShaders" and set it to false.

As for the memory part, you are either running too many mods for the amount of RAM/Memory you gave it, or you have too many heavy mods in your mod list.

Removing mods will solve the memory issue if there is some in there. Foamfix will also greatly improve your memory problem as it always does for me.