Help needed to amend Snow FLA

I need help to amend the snow FLA on the link below:

At the moment only a small amount of snow sticks to the bottom of the stage and then the snow continues falling but doesn’t stick. I need to be able to control how much snow initially sticks to the bottom of the stage (easily changable via a parameter), I need the snow at the bottom to build up in height, stop sticking but then it continutes to fall, hope that makes sense?

Happy to paypal $30 for solution to this, if you think it will take a while to do, still message me, I can pay more if the job requires a greater amount of time.