$wpdb query a post type within a specific taxonomy term while ordering posts by custom meta value?

You have a typo in orderby, and meta_value_num is only used as an orderby value, try this:

$args = array(
    'post_type' => 'event',
    'tax_query' => array(
        array(
            'taxonomy' => 'locations',
            'field' => 'id',
            'terms' => $location // location term id
        )
    ),
    'meta_key' => 'event_date',  // this meta field stores event date in yymmdd format
    'meta_value' => $today,  // this would be today's date in yymmdd format
    'meta_compare' => '>=',
    'posts_per_page' => $numberofposts, // this variable stores the number of posts I want to get
    'orderby'=> 'meta_value_num'
);