Array sorting by custom field date

You need to use the type parameter for custom field. Try this once

<?php 
$currentshowid = get_the_ID();
$today = date('Y-m-d');
$args = array(
              'meta_key' => 'show_id',
              'meta_value'  => $currentshowid,
              'orderby' => 'meta_value_num',
              'order' => ASC,
              'meta_query' =>array(
                                'relation' => 'AND',
                                array(
                                'key'       => 'date_end',
                                'value'   => $today,
                                'compare'   => '>=', 
                                'type'    => 'date'                               
                                ),
                            ),
          );