用as3.0做了以下代码，然后在主舞台调用，怎么让下雪停止，怎么在指定的帧停止
package  {
    import flash.display.MovieClip;
    import flash.events.Event;
    public class makeSnow extends MovieClip{

        public function makeSnow() {
            stage.addEventListener(Event.ENTER_FRAME,snowInit);
            function snowInit(e:Event){
                var mcSnow:snow=new snow();
                mcSnow.y=20;
                mcSnow.x=stage.stageWidth*Math.random();}
                addChild(mcSnow);
                if(mcSnow.y>350)
                {
                    mcSnow.removeEventListener(Event.ENTER_FRAME,snowInit);
                    
                }
                mcSnow.scaleX = mcSnow.scaleY = Math.random() * 2;
               
                var mcSpeed:Number=Math.random()*5;
                mcSnow.addEventListener(Event.ENTER_FRAME,snowFall);
                function snowFall(e:Event){
                    mcSnow.y+=mcSpeed;
                    mcSnow.rotation+=Math.random()*3;
                }
            
        }

    }
   
}