DESCRIPTION
Are you still using the default skyboxes that come with the SDK? A new set of skyboxes have been published to modding-assets.net, by Mr. Chop. They are categorized by time of day and weather conditions. It's free to use for all modders.
If you have XBLAH's Modding Tool, you can browse them and install them through Materials > Blueprints. If not, just download the VPKs directly from the website.
Check it out!
https://modding-assets.net/categories/source/textures/skies/