Photorealistic Rendering in Real-time

Dear Developers… I need some advice. I want to develop an app from grounds up that has a scene with rain. There are many thousand of moving rain particles. There is a requirement to be photorealistic.

My question is photorealistic animation of rain in real-time possible with current hardware? If so, which graphics cards maybe best to use? GPU with CUDA implementation better as opposed to using Shaders? Will Ray tracing work in real-time or raster-based rendering is way to go?

Thank you for pointers.

Take a look at OptiX capabilities. OptiX is a programmable ray tracing engine and may really come in handy for your purposes: http://www.nvidia.com/object/optix.html