Someone posted some cool snowflake shots last year. Was it
@crimbfighter ? or maybe
@goodguy ? I can't recall exactly. Try searching the forum for the thread and then asking them to describe their set-up.
I've posted a few such as these:
And just recently, this one:
To start, I you are going to need to go where the snow flakes are. As much as it sucks, I sit right out in the cold. Your gear can handle it, and as long as you dress for it, you probably can, too. Even if you hurry hurry hurry, the moment the flakes encounter warm air, they will start to melt and you're going to lose a lot of detail.
A couple thoughts for your setup. I would recommend setting it up outside, but under an overhang or something similar. You will get much better results shooting through a transparent material. I would suggest glass, no more than 1/8 inch thick and maybe 11x14 or similar because the thermal properties of glass will help retain the cold temps better than your acrylic will. It may be easiest to get a piece of pre-made picture frame glass. Put it outside or in the freezer to acclimate. Suspend the glass horizontally so the flakes don't fall off. Place an off camera flash underneath the glass and diffuse it. If you want to add some drama, use something like multi-colored tissue paper to diffuse the flash. Set your camera up on a tripod above the glass, prefocused near the minimum focusing distance, not quite at the minimum focusing distance so you still have a little bit of room to fine tune. Place a piece of paper on the glass that contains something, text or an image, on it. Adjust your tripod so the image or text on the paper is in focus. That should set you up nicely.
Next, catch your snow flakes on the glass. Easier said than done, but I've had luck with catching them as they fall. That also tended to have the best luck for capturing individual flakes. Sometimes the weather was also just not conducive for it, creating large clumps of flakes. The colder the weather the better because the flakes tend not to clump. I've also picked up handfulls of snow and tossed it up, just don't compact the snow at all when you pick it up. Once you have some flakes, use a magnifying glass to find one that meets your criteria, such as laying flat, or just looking cool. Lay the glass back on the setup and place a toothpick on the glass pointing to the flake you wanted to capture. This will help tremendously in finding that flake again in the viewfinder. Move the glass to find your toothpick and follow it to the flake and center in the frame. Use Liveview and zoom in. Fine tune your focus and fire away. You may need to adjust your exposure setting to find the right balance, but that should be a good starting place for you. Also try focus bracketing to make sure you got the best image possible.