addEventListener(Event.ENTER_FRAME, createSnow);

function createSnow(event:Event):void{
   var snowflake : Snowflake = new Snowflake();  snowflake.x = Math.random() * stage.stageWidth;
   snowflake.y = 0 ;
  addChild(snowflake);
   snowflake.addEventListener(Event.ENTER_FRAME, moveSnowflake);
}
 
function moveSnowflake(e:Event):void{
   if(e.target.y < stage.stageHeight){
     e.target.y += 10 + Math.random() * 5 ;
      e.target.alpha -= 0.015;
      e.target.scaleX = e.target.scaleY -= 0.01;
   }
  else{
      e.target.removeEventListener(Event.ENTER_FRAME,moveSnowflake);
      removeChild(e.target as Snowflake);
   }
}