Event.observe(window, 'load', check_usa, false);

function check_usa() {
	var d = new Date();
	var tzoffset = d.getTimezoneOffset();
	if (tzoffset > 180) { // it's not GMT-tz=d but d-tz=GMT
		new Effect.Appear('usa_prompt', {duration: 0.6});
	}
}