Undefined variable within nested IF statement

I am getting an underfined variable (headerHeight) when I try to call it inside a nested IF statement. If I put the alert outside of the nested IF statement it works but inside there it is undefined?

        var fixedHeader = $j('#fixed'); //check if ID is on page
        if(fixedHeader.length){
            var headerHeight = originalElement.height();
            var stickyHeaderThreshold = fixedHeader.offset().top + headerHeight - 47;
            $j(window).scroll(function() {
                if ($j('#this-page').length) {
                    //Do something
                } else { // Docviews
                    alert(headerHeight)
                }
            });
        }