var numClouds;
var clouds;
var CloudRate;

function manageClouds()
{
	if (cloudRate == 0)
	{
		//do nothing
	}
	else if (numClouds == 0)
	{
		clouds[0] = new Cloud();
	}
	else if (Math.random() < cloudRate/numClouds)
	{
		clouds[numClouds] = new Cloud();
	}
	for (var i = 0; i < numClouds; i++)
	{
		clouds[i].execute();
	}
}

function Cloud()
{
	this.x = context.canvas.width;
	this.y = Math.floor(Math.random() * (context.canvas.height/2 - 40) + 40);
	this.speed = -1.6 * Math.random() - .4;
	this.index = numClouds;

	numClouds++;

	this.execute = execute;
	this.move = move;
	this.drawSelf = drawSelf;
	this.removeSelf = removeSelf;
}

function execute()
{
	this.move();
	if (this.x < -154)
	{
		this.removeSelf();
	}
	this.drawSelf();
}

function move()
{
	this.x += this.speed;
}

function drawSelf()
{
	context.drawImage(cloudImg,this.x,this.y);
}

<b>function removeSelf()
{
var tempCloud = this;
	var i = this.index;
	while (i < numClouds - 1)
	{
		clouds[i] = clouds[i+1];
		i++;
	}
	clouds[i] = null;
	numClouds--;
	tempCloud = null;
}