Another way to do simultaneous animations if you want to call them separately (eg. from different code) is to use queue. Again, as with Tinister's answer you would have to use animate for this and not fadeIn:
$('.tooltip').css('opacity', 0);
$('.tooltip').show();
...
$('.tooltip').animate({opacity: 1}, {queue: false, duration: 'slow'});
$('.tooltip').animate({ top: "-10px" }, 'slow');