The stereoscopic rendering of rain has been previously studied. We extend the behavior and distribution of rainfall to include photorealistic stereo rendering of rain and snow precipitation at video frame rates. We ignore stereo rendering optimization and concentrate on the visual factors necessary to produce photorealistic output. The experimental method uses a series of controlled human experiments where participants are presented with video clips and still photos of real precipitation. The stimuli vary along three visual factors: particle numbers, particle size, and motion. The goal is to determine the statistical ranking and importance of these visual factors for producing a photorealistic output. The experiments are extended to investigate if stereo improves photorealism. Additionally, experimental stimuli include post-processing on rendered output to produce variable lighting, glow, and fog effects to study their impact on photorealism as the stereo camera moves in the scene. The results demonstrate that the visual factors for photorealism can be ranked as more sensitive to particle numbers and motion than to particle size. Varying light, glow, and fog effects contribute towards photorealism independent of stereo. Future research will exploit the geometric symmetry of the stereoscopic image pairs to render precipitation while maintaining realtime frame rates.