I'm not sure how the motd works in cs 1.6, and whether it is capable of rendering snow, but I'm listing a few light examples (in javascript)
https://jsfiddle.net/loktar/UdyN6/
http://jsfiddle.net/dodopod/5SzEz/ not too realistic but probably the easiest to render
This:
https://jsfiddle.net/osc9yrL2/15/
is a simplified version of this:
https://jsfiddle.net/osc9yrL2/
Also check this link with more snow, but not sure whether they will render on motd:
https://engageinteractive.co.uk/blog...n-snow-effects
I definitely don't recommend you use 4 and 5 since they use external files.
Now, I'm not sure if motd is even capable of running javascript since I never got to try it. The closest I've got to using the motd is a few simple html lines.
This seems to be fully in css
https://codepen.io/NickyCDK/pen/AIonk
And this one
https://codepen.io/jpschwinghamer/pen/QwwbgO