This is a paid asset, but now you can download OverCloud Free.
Detail this asset from Unity Asset Store: Original Link
OverCloud v1.10 (Latest version)
“If possible, please buy the package to support the developer”
OverCloud provides a complete, scalable solution for rendering a realistic, volumetric sky from any camera position and angle above the horizon. It is perfect for flight simulators, huge landscapes, or any developer looking for a simple-to-use, dynamic sky.
Unity default rendering pipeline (forward or deferred). Compute shaders (DX11).
Volumetric cloud plane
Accelerated by a unique particle-grid rendering method, which only spends fill rate where there’s actually cloud coverage. Supports advanced effects such as ray-marched, energy-conserving lighting, cloud shadows, cloud ambient occlusion and cloud coverage probing on the CPU.
Physically based atmospheric scattering
OverCloud includes a tried and tested pre-calculated atmospheric scattering solution which is used to render the sky and aerial perspective. It also automatically fades the scene into the skybox based on the far clip plane, so your world always blends smoothly with the atmosphere.
True volumetric height fog
OverCloud supports a global height-based volumetric fog effect, which perfectly blends with the atmospheric scattering. Move the camera into the volume and watch the sky disappear above, or fly above the clouds during heavy weather to catch a glimpse of a clear sky.
OverCloud generates crepuscular rays which take into account both cloud and world shadows. Additionally, it supports volumetric point and spotlights which mix perfectly with the global fog and clouds.
Physically based time of day
Set year, date, time, latitude and longitude and watch the sky position itself correctly. Sun and moon elements are properly rendered in the skybox with physical sizes, it even supports solar and lunar eclipses.
Fully compatible with scene view
All effects support rendering in the scene camera (via main camera hook) so you can tweak the result without having to run the game.
Preset-based weather system
Tweak a number of parameters for the clouds and sky. Smoothly fade parameters between different presets. Supports adding your own float variables which can be used to drive custom effects.
Dynamic surface wetness
(Limited to deferred rendering path or custom shaders)
OverCloud supports modifying albedo and gloss of surfaces below rainy clouds, and can dynamically occlude wetness from surfaces that should be protected from rain (such as inside a building or under a protruding cliff). It also features animated rain ripples.
OverCloud has a scalable quality system which is tweakable per-camera. Want to render just the clouds or atmospheric scattering? Want to have high-resolution clouds in your main camera but low-res ones in another? No problem!
Made for VR
OverCloud was born out of the need for a robust volumetric sky solution for a virtual reality project. All effects are stereo-compatible and VR performance has been at the forefront of the development at all times (supports multi-pass and single-pass stereo).
Forward or deferred
OverCloud works in both forward and deferred rendering paths. Some effects are limited to deferred (cloud AO and dynamic wetness) but can be implemented in forward if you are using custom shaders.
Full Source Code
All code is written in C# and HLSL, and is fully accessible and commented.
Floating origin support
OverCloud features a set of functions for moving the rendering origin of the world, a must if you are creating huge worlds in Unity.