I work on Christmas and holiday productions a lot and it is hard to find long clips of snow. Here is one minute of the effect, originally created in 6K. You can overlay it on top of your footage using the 'screen' compositing effect. This version has a big area of a 'ground' or 'floor' where the snowflakes hit and melt away. If you zoom in on the footage you can move it around to shift the location of this floor to match your shot.