Available in two colors.
NOTE: This size is recommended for cameras that are 27" (68cm) or less from the rear of the camera body to the front of the lens hood.
The Storm Jacket Pro model has an opening at the bottom that makes it easier to get your hand inside to focus the lens manually or to mount the camera on a tripod or monopod. The velcro opening is several inches long to facilitate a wide variety of configurations, quick-release plates, and gimbals. The opening at the bottom is the only difference between Pro and Standard models.
Pro Models are not available in small and only come in Black and Camouflage colors.
The model or brand of SLR that you own does not make any difference when choosing the size of the cover. In fact, all Storm Jackets have the same internal diameter (8") for the front and rear openings, so the only difference between S, M, L, XL, XXL is the length of the cover from front to back. In other words, what matters when selecting a size is the length from the rear of your camera's body to the front of the lens hood when the zoom is fully-extended.
(tripod head seen in photo is not included)