The script goes on your Area OnEnter, the variables should be explained in the top notes

Code:

//hc_weather //////////////////////////////////////////////////////// // // Sets the weather of an area determined by variables // // Author: Hellcow // Last modified: March 05, 2007 //////////////////////////////////////////////////////// // Variable - WEATHER_TYPE - int //  0 = Rain //  1 = Snow //  2 = Lightning // // Variable - WEATHER_POWER - int //  0 = No Power //  1 = Weak //  2 = Light //  3 = Medium //  4 = Heavy //  5 = Stormy // void main() { int nWeatherType = GetLocalInt(OBJECT_SELF, "WEATHER_TYPE"); int nPower = GetLocalInt(OBJECT_SELF, "WEATHER_POWER"); int nWeather; int nPowerChoice;     switch ( nWeatherType )     {         case 0:     // Rain             nWeather = WEATHER_TYPE_RAIN;             break;         case 1:     // Snow             nWeather = WEATHER_TYPE_SNOW;             break;         case 2:     // Lightning             nWeather = WEATHER_TYPE_LIGHTNING;             break;     }            switch ( nPower )     {         case 0:                  nPowerChoice = WEATHER_POWER_OFF;             break;         case 1:                  nPowerChoice = WEATHER_POWER_WEAK;             break;         case 2:                  nPowerChoice = WEATHER_POWER_LIGHT;             break;         case 3:                  nPowerChoice = WEATHER_POWER_MEDIUM;             break;         case 4:                  nPowerChoice = WEATHER_POWER_HEAVY;             break;                           case 5:                  nPowerChoice = WEATHER_POWER_STORMY;             break;      }    SetWeather(OBJECT_SELF, nWeather, nPowerChoice); }

Nice...
Thou only rains work, no VFX for snow and lightning, but that is a Obsedian bug or leaveout, I guess.

Snow was added in MotB expansion (Couldn't say if it's updated in NWN2 but I imagine it would be)