For example, here is the script for mohdm1 with it added:
// SOUTHERN FRANCE
// ARCHITECTURE: SENN
// SCRIPTING: POWZER
main:
// set scoreboard messages
setcvar "g_obj_alliedtext1" "Southern France"
setcvar "g_obj_alliedtext2" ""
setcvar "g_obj_alliedtext3" ""
setcvar "g_obj_axistext1" ""
setcvar "g_obj_axistext2" ""
setcvar "g_obj_axistext3" ""
setcvar "g_scoreboardpic" "mohdm1"
// call additional stuff for playing this map round based is needed
if(level.roundbased)
thread roundbasedthread
level waitTill prespawn
//*** Precache Dm Stuff
exec global/DMprecache.scr
level.script = maps/dm/mohdm1.scr
exec global/ambient.scr mohdm1
//exec global/ambient.scr mohdm2
//$world farplane 5000
//$world farplane_color (.333 .333 .329)
level waittill spawn
level.rain_speed = "32"
level.rain_speed_vary = "16"
level.rain_length = "2"
level.rain_width = "1"
level.rain_density = ".2"
level.rain_slant = "250"
level.rain_min_dist = "1800"
level.rain_numshaders = 12
level.rain_shader = "textures/snow0"
end
//-----------------------------------------------------------------------------
roundbasedthread:
// Can specify different scoreboard messages for round based games here.
level waitTill prespawn
level waittill spawn
// set the parameters for this round based match
level.dmrespawning = 0 // 1 or 0
level.dmroundlimit = 5 // round time limit in minutes
level.clockside = kills // set to axis, allies, kills, or draw
level waittill roundstart
end
But obviously your map script would be your_map_name.scr
By all means play around with some of the numbers to change the snow slant, speed, density etc...