Hello ,
Thank you for posting your question in the community and it should work if you follow the setting shown below (The Season slider should be in the middle of the snowman).
if that does not work I was hoping you could report a bug as there should be a way to set it without rain. Here is the link to report a bug: https://twinmotionhelp.epicgames.com/s/case-community-page
Kind regards,
Vincent B.