I looked what screen effect is this.
It's particle effect, you can find from Hammer editor (using entity "info_particle_system").
Code:
"snow_hit_player_screeneffect"
"snow_hit_player_screeneffect_bb"
"snow_hit_player_screeneffect_b"
But problem is in "info_particle_system" (in VScript
DispatchParticleEffect(string, Vector, Vector))
this effect can't execute on specific targets.
This function use position and angle, where it will spawn particle and show to all players. (And can be attach to player if like).
Because these snow particles are
screeneffect, it will show to everyone when you create/activate this, just single one.
So, using
event "snowball_hit_player_face" work great.
Maybe this event trigger -> to create particle effect inside player game, client side. Never know.
Or I haven't find other way to create particle effect.
*edit
Maybe tempent are for client side particles...