$args = array(
   'post_type' => 'post_type',
   'order'     => 'ASC',
   'meta_query' => array( array(
      'key'     => 'date_key',
      'value'   => date("Y-m-d"),
      'compare' => '>=',
      'type'    => 'DATE'
    ) )
);
$query = new WP_Query($args);